Imaging system, imaging apparatus, portable terminal apparatus, onboard apparatus, medical apparatus and method of manufacturing the imaging system

ABSTRACT

An imaging system is provided and includes: an imaging lens; an imaging device; a coefficient storage section; and a signal processing section. When a maximum diameter of an effective region of a point image projected onto a light receiving surface of the imaging device through the imaging lens  10  is a size covering three or more pixels, a restoration coefficient corresponding to a state of the point image expressed by first image data output from the imaging device is stored in the coefficient storage unit. The signal processing section executes restoration processing on the first image data output from the imaging device by utilizing the restoration coefficient stored in the coefficient storage unit, the restoration processing being executed to generate second image data equivalent to the first image data output from the imaging device when the resolving power of the imaging lens is higher. The imaging lens has a first lens group, which includes at least one lens and has a positive power, and a second lens group, which includes at least one lens and in which a lens positioned closest to the image side has a negative power, in order from the object side.

This application is based on and claims priority under 35 U.S.C §119from Japanese Patent Application No. 2007-298146, filed on Nov. 16,2007, the entire disclosure of which is herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an imaging system capable of improvingthe quality of image data obtained by imaging an optical image of asubject, an imaging apparatus including the imaging system, a portableterminal apparatus including the imaging system, an onboard apparatusincluding the imaging system, a medical apparatus including the imagingsystem, and a method for manufacturing an imaging system.

2. Description of Related Art

An imaging system that forms an optical image of a subject, which isfocused on a light receiving surface through an imaging lens, byutilizing an imaging device, such as a CCD or a CMOS device, having thelight receiving surface on which a plurality of light receiving pixelsare two-dimensionally arrayed is known.

As an example of such an imaging system, an onboard camera or a portablecellular phone camera in which an imaging system having an imaging lensdesigned such that the depth of field increases is attached directly ona circuit board has already put to practical use (refer toJP-A-2007-147951). In addition, an onboard camera or a portable cellularphone camera with high performance in which an imaging system, in whichthe number of light receiving pixels of an imaging device is increasedand the resolving power of an imaging lens is improved, is mounted isalso known. Among such onboard cameras or portable cellular phonecameras with high performance capable of obtaining high-resolutionimages, one in which the resolving power of an imaging lens is close toa diffraction limited is also known.

However, in manufacturing an imaging system having such an imaging lenscapable of forming an image with high resolution, it is difficult toincrease the yield due to difficulties in manufacture. That is, sinceimage data allowing an image having an intended resolution to be formedcannot be generated, there is a possibility that many imaging systemswill be out of a production line for readjustment or reassembly. Inaddition, an imaging system removed from the production line isreproduced such that and image data capable of forming an image with theintended resolution can be generated by specifying the cause andperforming modification.

However, there are various causes of reducing the resolution of an imageexpressed by image data output from an imaging system. For example,various causes, such as shape errors (surface shape error, thicknesserror, and eccentric error of a lens) of an individual lens used to forman imaging lens, assembly and adjustment errors of an imaging lens(shift error and tilt error of a lens and air space error betweenlenses), and a positional error of an imaging device with respect to animaging lens, may be considered. For this reason, there is a problemthat a cost is significantly increased for reproduction to an imagingsystem capable of generating high-quality image data, which allows animage with the intended resolution to be formed, by specifying a causeof the reduction in resolution and performing readjustment andreassembly.

SUMMARY OF THE INVENTION

An object of an illustrative, non-limiting embodiment of the inventionis to provide an imaging system capable of easily improving the qualityof image data obtained by imaging an optical image projected onto alight receiving surface, an imaging apparatus including the imagingsystem, a portable terminal apparatus including the imaging system, anonboard apparatus including the imaging system, a medical apparatusincluding the imaging system, and a method for manufacturing an imagingsystem.

According to an aspect of the invention, there is provided an imagingsystem including:

an imaging lens;

an imaging device that has a light receiving surface on which aplurality of light receiving pixels are two-dimensionally arrayed andthat forms first image data based on an optical image of a subjectprojected onto the light receiving surface through the imaging lens andoutputs the first image data expressing the subject;

coefficient storage means for being configured to store a restorationcoefficient corresponding to a state of a point image, which isprojected onto the light receiving surface through the imaging lens andis expressed by the first image data output from the imaging device,when a maximum diameter of an effective region of the point image is asize covering three or more pixels; and

signal processing means for executing restoration processing on thefirst image data by using the restoration coefficient, the restorationprocessing being executed to generate second image data equivalent tothe first image data output from the imaging device when the resolvingpower of the imaging lens is higher,

wherein the signal processing means executes the restoration processingin a condition where a pixel region covering total nine or more pixelsincluding three or more pixels in a vertical direction and three or morepixels in a horizontal direction on the light receiving surface is setas a minimum unit, and

the imaging lens comprises: in order from an object side of the imaginglens, a first lens group which includes at least one lens and has apositive power; and a second lens group which includes at least one lensand in which a lens positioned closest to an image side of the imaginglens has a negative power.

The “coefficient storage means being configured to store a restorationcoefficient” means that the coefficient storage means will store arestoration coefficient.

The coefficient storage means may be configured to store the restorationcoefficient individually calculated for each corresponding imagingsystem.

In addition, the coefficient storage means may be configured to storethe restoration coefficient which is selected corresponding to a stateof the point image expressed by the first image data among candidates ofrestoration coefficients corresponding to respective states of pointimages classified into a plurality of types.

In addition, the coefficient storage means may be configured to store acorrection-completed restoration coefficient obtained by furthercorrection of the restoration coefficient according to a state of thepoint image expressed by the first image data, the restorationcoefficient being selected corresponding to the state of the point imageamong candidates of a plurality of types of restoration coefficientscorresponding to respective states of point images classified into aplurality of types.

The imaging system may further include restoration coefficientacquisition means for acquiring the restoration coefficient and storingthe acquired restoration coefficient in the coefficient storage section.

The signal processing section may execute the restoration processingwith a minimum pixel region, which includes the entire effective regionof the point image projected onto the light receiving surface, as aminimum unit.

The signal processing means may execute the restoration processing suchthat the size of the effective region of the point image in an imageexpressed by the second image data is smaller than the size of theeffective region of the point image in an image expressed by the firstimage data.

The lens surface positioned closest to the image side in the second lensgroup may have an off-axis inflection point, may have a concave surfaceon the image side at the on-axis of the lens surface and is convextoward the image side in the periphery of the lens surface, or maysatisfy the following conditional expression (1).

0.5H<h<H   (1)

Here, H is an effective radius of the lens surface positioned closest tothe image side in the second lens group, and h is a distance from anoff-axis inflection point of the lens surface positioned closest to theimage side in the second lens group to the optical axis.

Here, the inflection point is a point on the lens surface. When atangential plane at this point is perpendicular to the optical axis C (Zaxis), the point is called an inflection point. Moreover, an inflectionpoint other than the point crossing the optical axis on the lens surfaceis called an off-axis inflection point.

The imaging lens may be configured to include three single lenses.

The first lens group may be configured to include two single lenses andthe second lens group may be configured to include one single lens. Onepositioned on the object side of the two single lenses included in thefirst lens group may have a positive power and an object-side surface ofthe single lens may be convex toward the object side, and the other onepositioned on the image side of the two single lenses may have animage-side surface which is convex toward the image side.

The imaging lens may be configured to include four single lenses.

The first lens group may be configured to include three single lensesand the second lens group may be configured to include one single lens.The first one positioned closest to the object side among the threesingle lenses included in the first lens group may have a positive powerand an object-side surface of the first single lens may be convex towardthe object side. The second one adjacent to the first single lens amongthe three single lenses may have a negative power and an image-sidesurface of the second single lens may be convex toward the image side,and the third one positioned closest to the image side among the threesingle lenses may have a positive power.

According to an aspect of the invention, there is provided an imagingapparatus including the imaging system described above.

According to an aspect of the invention, there is provided a portableterminal apparatus including the imaging system described above.

According to an aspect of the invention, there is provided an onboardapparatus including the imaging system described above.

According to an aspect of the invention, there is provided a medicalapparatus including the imaging system described above.

According to an aspect of the invention, there is provided an imagingsystem includes:

an imaging lens;

an imaging device that has a light receiving surface on which aplurality of light receiving pixels are two-dimensionally arrayed andthat forms first image data based on an optical image of a subjectprojected onto the light receiving surface through the imaging lens andoutputs the first image data expressing the subject;

coefficient storage means storing a restoration coefficientcorresponding to a state of a point image, which is projected onto thelight receiving surface through the imaging lens and is expressed by thefirst image data output from the imaging device, when a maximum diameterof an effective region of the point image is a size covering three ormore pixels; and

signal processing means for executing restoration processing on thefirst image data by using the restoration coefficient, the restorationprocessing being executed to generate second image data equivalent tothe first image data output from the imaging device when the resolvingpower of the imaging lens is higher,

wherein the signal processing means executes the restoration processingin a condition where a pixel region covering total nine or more pixelsincluding three or more pixels in a vertical direction and three or morepixels in a horizontal direction on the light receiving surface is setas a minimum unit, and

the imaging lens comprises: in order from an object side of the imaginglens, a first lens group which includes at least one lens and has apositive power; and a second lens group which includes at least one lensand in which a lens positioned closest to an image side of the imaginglens has a negative power.

According to an aspect of the invention, there is provided a method formanufacturing an imaging system that includes:

an imaging lens, wherein the imaging lens comprises: in order from anobject side of the imaging lens, a first lens group which includes atleast one lens and has a positive power; and a second lens group whichincludes at least one lens and in which a lens positioned closest to animage side of the imaging lens has a negative power;

an imaging device that has a light receiving surface on which aplurality of light receiving pixels are two-dimensionally arrayed andthat forms first image data based on an optical image of a subjectprojected onto the light receiving surface through the imaging lens andoutputs the first image data expressing the subject;

coefficient storage means storing a restoration coefficientcorresponding to a state of a point image, which is projected onto thelight receiving surface through the imaging lens and is expressed by thefirst image data output from the imaging device, when a maximum diameterof an effective region of the point image is a size covering three ormore pixels; and

signal processing means for executing restoration processing on thefirst image data by utilizing the restoration coefficient, therestoration processing being executed to generate second image dataequivalent to the first image data output from the imaging device when aresolving power of the imaging lens is higher, wherein the signalprocessing section executes the restoration processing in a conditionwhere a pixel region covering total nine or more pixels including threeor more pixels in a vertical direction and three or more pixels in ahorizontal direction on the light receiving surface is set as a minimumunit,

the method including projecting the point image onto the light receivingsurface of the imaging device through the imaging lens to cause thecoefficient storage section to store the restoration coefficientcorresponding to a state of the point image expressed by the first imagedata output from the imaging device.

The restoration coefficient may be individually calculated for eachcorresponding imaging system.

The restoration coefficient may be selected corresponding to a state ofthe point image expressed by the first image data among candidates ofeach restoration coefficient corresponding to each of states of pointimages classified into a plurality of types.

In addition, the restoration coefficient may be obtained by furthercorrection of the restoration coefficient according to a state of thepoint image expressed by the first image data, the restorationcoefficient being selected corresponding to the state of the point imageamong candidates of a plurality of types of restoration coefficientscorresponding to respective states of point images classified into aplurality of types.

The maximum diameter of the effective region of the point imageprojected onto the light receiving surface may be assumed as a diameterof the effective region in a direction in which the effective region ofthe point image projected onto the light receiving surface includes alargest number of light receiving pixels, and “when the maximum diameterof the effective region of the point image projected onto the lightreceiving surface is a size covering three or more pixels” may beassumed as “when the effective region has a size covering three or morepixels of light receiving pixels in a direction in which the maximumdiameter of the effective region of the point image projected onto thelight receiving surface is a size covering three or more pixels”.

The “effective region of a point image” means a region having a lightintensity of 1/e² (about 13.5%) of a peak intensity in the lightintensity distribution indicating the point image.

In addition, image restoration processing disclosed in paragraphs (0002to 0016) of JP-A-2000-123168 may be adopted as the “restorationprocessing”. Moreover, in execution of the restoration processing, forexample, a technique disclosed in Non-patent Document “title “KernelWiener Filter”, Yoshikazu Washizawa and Yukihiko Yamashita, 2003Workshop on Information-Based Induction Sciences, (IBIS2003), Kyoto,Japan, Nov. 11-12, 2003”, which will be described, may be applied.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention will appear more fully upon considerationof the exemplary embodiment of the invention, which are schematicallyset forth in the drawings, in which:

FIG. 1 is a block diagram showing a schematic configuration of animaging system of the invention and a method for manufacturing animaging system according to an exemplary embodiment of the invention;

FIG. 2A is a view showing the light intensity distribution of a pointimage, and FIG. 2B is a view showing a point image projected onto alight receiving surface;

FIG. 3A is a view showing an image of a point image displayed in animage expressed by first image data, and FIG. 3B is a view showing animage of a point image displayed in an image expressed by second imagedata;

FIG. 4A is a view showing the light intensity distribution of a pointimage to be projected onto a light receiving surface when the resolvingpower of an imaging lens is higher, and FIG. 4B is a view showing eachpixel region of a light receiving pixel that forms a light receivingsurface and a point image to be projected onto the light receivingsurface when the resolving power of the imaging lens is higher;

FIG. 5 is a view showing a restoration coefficient acquisition apparatusin a second example;

FIG. 6 is a view showing a restoration coefficient acquisition apparatusin a third example;

FIG. 7 is a view showing an imaging system including a restorationcoefficient acquisition apparatus;

FIG. 8 is a view showing an imaging system including a signal processingunit that has a restoration coefficient acquisition apparatus and acoefficient storage unit;

FIG. 9 is a view showing a change in a maximum diameter of an effectiveregion of a point image, which is an optical image of an object point,projected onto a light receiving surface when the object point is madeto move in an optical-axis direction;

FIG. 10 is a view showing a change in a value of MTF characteristicsregarding an optical image of an object point projected onto a lightreceiving surface when the object point is made to move in anoptical-axis direction;

FIG. 11 is a cross-sectional view showing a schematic configuration ofan imaging lens disposed in an imaging system in Example 1;

FIGS. 12A to 12D are views illustrating a change in a value of MTFcharacteristics when a light receiving surface is defocused,specifically, FIG. 12A is a view showing a change in a value of MTFcharacteristics in a spatial frequency of 20 line/mm, FIG. 12B is a viewshowing a change in a value of MTF characteristics in a spatialfrequency of 30 line/mm, FIG. 12C is a view showing a change in a valueof MTF characteristics in a spatial frequency of 40 line/mm, and FIG.12D is a view showing a change in a value of MTF characteristics in aspatial frequency of 50 line/mm;

FIG. 13 is a cross-sectional view showing the schematic configuration ofan imaging lens disposed in an imaging system in Example 2;

FIGS. 14A to 14D are views illustrating a change in a value of MTFcharacteristics when a light receiving surface is defocused,specifically, FIG. 14A is a view showing a change in a value of MTFcharacteristics in a spatial frequency of 20 line/mm, FIG. 14B is a viewshowing a change in a value of MTF characteristics in a spatialfrequency of 30 line/mm, FIG. 14C is a view showing a change in a valueof MTF characteristics in a spatial frequency of 40 line/mm, and FIG.14D is a view showing a change in a value of MTF characteristics in aspatial frequency of 50 line/mm;

FIG. 15 is a cross-sectional view showing the schematic configuration ofan imaging lens disposed in an imaging system in Example 3;

FIGS. 16A to 16D are views illustrating a change in a value of MTFcharacteristics when a light receiving surface is defocused,specifically, FIG. 16A is a view showing a change in a value of MTFcharacteristics in a spatial frequency of 20 line/mm, FIG. 16B is a viewshowing a change in a value of MTF characteristics in a spatialfrequency of 30 line/mm, FIG. 16C is a view showing a change in a valueof MTF characteristics in a spatial frequency of 40 line/mm, and FIG.16D is a view showing a change in a value of MTF characteristics in aspatial frequency of 50 line/mm;

FIG. 17 is a view showing an aberration of an imaging lens in Example 1;

FIG. 18 is a view showing an aberration of an imaging lens in Example 2;

FIG. 19 is a view showing an aberration of an imaging lens in Example 3;

FIG. 20 is a cross-sectional view showing a schematic configuration ofan imaging lens disposed in an imaging system in a comparative example;

FIGS. 21A to 21D are views illustrating a change in a value of MTFcharacteristics when a light receiving surface is defocused,specifically, FIG. 21A is a view showing a change in a value of MTFcharacteristics in a spatial frequency of 20 line/mm, FIG. 21B is a viewshowing a change in a value of MTF characteristics in a spatialfrequency of 30 line/mm, FIG. 21C is a view showing a change in a valueof MTF characteristics in a spatial frequency of 40 line/mm, and FIG.21D is a view showing a change in a value of MTF characteristics in aspatial frequency of 50 line/mm;

FIG. 22 is a view showing an automobile in which an onboard apparatusincluding an imaging system is mounted;

FIG. 23 is a view showing a portable cellular phone which is a portableterminal apparatus including an imaging system; and

FIG. 24 is a view showing an endoscope apparatus which is a medicalapparatus including an imaging system.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

An imaging system according to a first exemplary embodiment of theinvention includes: the coefficient storage means for being configuredto store a restoration coefficient corresponding to a state(hereinafter, referred to as a blur state of a point image) of a pointimage, which is projected onto the light receiving surface through theimaging lens and is expressed by the first image data output from theimaging device, when the maximum diameter of the effective region of thepoint image is a size covering three or more pixels; and the signalprocessing means for executing the restoration processing on the firstimage data by using the restoration coefficient, the restorationprocessing being executed to generate the second image data equivalentto the first image data output from the imaging device when theresolving power of the imaging lens is higher. In addition, the signalprocessing means executes the restoration processing in a conditionwhere the pixel region covering total nine or more pixels includingthree or more pixels in the vertical direction and three or more pixelsin the horizontal direction on the light receiving surface is set as theminimum unit. In addition, the imaging lens includes: in order from anobject side of the imaging lens, a first lens group which includes atleast one lens and has a positive power; and a second lens group whichincludes at least one lens and in which a lens positioned closest to animage side of the imaging lens has a negative power. Therefore, sincethe restoration processing using the restoration coefficient can beexecuted by storing the restoration coefficient in the coefficientstorage section, the quality of image data obtained by imaging anoptical image projected onto the light receiving surface can be easilyimproved.

That is, when the resolution of an image expressed by the first imagedata output from the imaging system does not reach an intended level, itis not necessary to specify the cause and readjust or reassemble theimaging lens unlike the related art. That is, the second image data thatexpresses an image having an intended resolution can be obtained only bystoring a restoration coefficient corresponding to a blur state of apoint image imaged in the imaging system in the coefficient storagemeans and performing restoration processing (image processing) on thefirst image data. As a result, the quality of image data obtained byimaging an optical image projected onto the light receiving surface canbe easily improved.

The reason why the “state of a point image” is called the “blur state ofa point image” is that the image quality of a point image projected ontothe light receiving surface through the imaging lens and the imagequality of a point image expressed by the first image data obtained byimaging the point image deteriorate a little due to an influence of lensaberration and the like as compared with a subject which becomes anobject point corresponding to the point image. That is, for example,assuming that a subject is a resolving power chart, the resolution of animage of the resolving power chart projected onto a light receivingsurface through an imaging lens and the resolution of an image of theresolving chart expressed by the first image data obtained by imagingthe image of the resolving power chart become lower than the resolutionof the resolving power chart that becomes the subject. In addition, the“state of a point image” or the “blur state of a point image” mainlyindicates a degradation state of the resolution of the point image.

Furthermore, when the coefficient storage means is made to store arestoration coefficient individually calculated for each correspondingimaging system, the restoration coefficient can be calculated moreaccurately and the restoration processing can be executed moreaccurately. Accordingly, the quality of image data obtained by imagingan optical image projected onto the light receiving surface can beimproved more reliably.

In addition, when the coefficient storage means is made to store arestoration coefficient which is selected corresponding to a blur stateof a point image expressed by the first image data among candidates ofeach restoration coefficient corresponding to each of blur states ofpoint images classified into a plurality of types, the restorationcoefficient can be set more easily compared with the case in which arestoration coefficient is individually calculated for eachcorresponding imaging system.

Here, when the coefficient storage means is made to store acorrection-completed restoration coefficient obtained by furthercorrection of a restoration coefficient, which is selected correspondingto a blur state of the point image expressed by the first image dataamong candidates of a plurality of types of restoration coefficientscorresponding to each of blur states of point images classified into aplurality of types, according to a blur state of the point image, therestoration coefficient can be acquired more easily while suppressing areduction in accuracy in calculating the restoration coefficientcompared with the case in which a restoration coefficient isindividually calculated for each corresponding imaging system.

Furthermore, when the imaging system is made to include the restorationcoefficient acquisition means for acquiring the restoration coefficientand storing the acquired restoration coefficient in the coefficientstorage means, the restoration coefficient can be acquired morereliably.

Furthermore, when the signal processing means is made to execute therestoration processing with a minimum pixel region, which includes theentire effective region of the point image projected onto the lightreceiving surface, as a minimum unit, it is possible to suppress anincrease in amount of operation for executing the restoration processingand to efficiently execute the restoration processing.

Furthermore, when the signal processing means is made to execute therestoration processing such that the size of the effective region of thepoint image in an image expressed by the second image data is smallerthan the size of the effective region of the point image in an imageexpressed by the first image data, the quality of image data obtained byimaging an optical image projected onto the light receiving surface canbe improved more reliably.

In addition, when the lens surface positioned closest to the image sidein the second lens group is made to have an off-axis inflection point,to be concave toward the image side at the on-axis of the lens surfaceand convex toward the image side in the periphery of the lens surface,or to satisfy 0.5H<h<II which is the conditional expression (1),telecentricity of the imaging lens can be improved more reliably. As aresult, the quality of the first image data expressing a subject can beimproved more reliably.

Furthermore, when the imaging lens is configured to include only threesingle lenses in a condition where the first lens group includes twosingle lenses and the second lens group includes one single lens, onepositioned on the object side of the two single lenses included in thefirst lens group has a positive power and an object-side surface of thesingle lens is convex toward the object side, and the other onepositioned on the image side of the two single lenses has an image-sidesurface which is convex toward the image side, the telecentricity of theimaging lens can be improved more reliably. As a result, the quality ofthe first image data expressing a subject can be improved more reliably.

Furthermore, when the imaging lens is configured to include four singlelenses in a condition where the first lens group includes three singlelenses and the second lens group includes one single lens, the first onepositioned closest to the object side among the three single lensesincluded in the first lens group has a positive power and an object-sidesurface of the single lens is convex toward the object side, the secondone adjacent to the first single lens among the three single lenses hasa negative power and an image-side surface of the second single lens isconvex surface toward the image side, and the third one positionedclosest to the image side among the three single lenses has a positivepower, the telecentricity of the imaging lens can be improved morereliably in the same manner as described above. As a result, the qualityof the first image data expressing a subject can be improved morereliably.

Each of the imaging apparatus, portable terminal apparatus, onboardapparatus, and medical apparatus of the invention includes the imagingsystem described above. Therefore, the quality of image data obtained byimaging an optical image projected onto a light receiving surface can beimproved more reliably as described above.

An imaging system according to a second exemplary embodiment of theinvention includes: the coefficient storage means storing a restorationcoefficient corresponding to a state of a point image, which isprojected onto the light receiving surface through the imaging lens andis expressed by the first image data output from the imaging device,when the maximum diameter of the effective region of the point image isa size covering three or more pixels; and the signal processing meansfor executing the restoration processing on the first image data byusing the restoration coefficient, the restoration processing beingexecuted to generate the second image data equivalent to the first imagedata output from the imaging device when the resolving power of theimaging lens is higher. In addition, the signal processing meansexecutes the restoration processing in a condition where the pixelregion covering total nine or more pixels including three or more pixelsin the vertical direction and three or more pixels in the horizontaldirection on the light receiving surface is set as the minimum unit. Inaddition, the imaging lens includes: in order from an object side of theimaging lens, a first lens group which includes at least one lens andhas a positive power; and a second lens group which includes at leastone lens and in which a lens positioned closest to an image side of theimaging lens has a negative power. Therefore, the quality of image dataobtained by imaging an optical image projected onto the light receivingsurface can be easily improved, as in the above first embodiment.

According to a method for manufacturing an imaging system in anexemplary embodiment of the invention, the imaging system includes:coefficient storage means storing a restoration coefficientcorresponding to a state of a point image, which is projected onto thelight receiving surface through the imaging lens and is expressed by thefirst image data output from the imaging device, when the maximumdiameter of the effective region of the point image is a size coveringthree or more pixels; and signal processing means for executingrestoration processing on the first image data by using the restorationcoefficient, the restoration processing being executed to generate thesecond image data equivalent to the first image data output from theimaging device when the resolving power of the imaging lens is higher,and the signal processing means executes the restoration processing in acondition where the pixel region covering total nine or more pixelsincluding three or more pixels in the vertical direction and three ormore pixels in the horizontal direction on the light receiving surfaceis set as the minimum unit. In addition, the imaging lens includes: inorder from an object side of the imaging lens, a first lens group whichincludes at least one lens and has a positive power; and a second lensgroup which includes at least one lens and in which a lens positionedclosest to an image side of the imaging lens has a negative power.Further, the point image is projected onto the light receiving surfaceof the imaging device through the imaging lens, and a restorationcoefficient corresponding to a state of the point image expressed by thefirst image data output from the imaging device is stored in thecoefficient storage means. Accordingly, the second imaging system can bemanufactured efficiently.

For example, even if the resolving power of an image expressed by imagedata output from the imaging system does not reach an intended level dueto a manufacturing problem, reproduction processing of the imagingsystem for increasing the resolving power of an image can be easilyexecuted compared with that in the relate art. That is, sincerestoration processing for increasing the quality of image data outputfrom the imaging system can be easily executed by the imaging system inwhich a restoration coefficient is stored in the coefficient storagemeans, an imaging system in which the resolving power of an image doesnot reach an intended level can be reproduced to one in which theresolving power of an image with the intended level can be easilyobtained. Accordingly, an imaging system can be manufacturedefficiently.

That is, since the restoration processing for improving the quality ofimage data output from the imaging system in which the restorationcoefficient is stored in the coefficient storage means can be easilyexecuted, an imaging system can be easily reproduced. As a result, theimaging system can be manufactured efficiently.

In addition, in the case when the imaging system is produced in largequantities, a larger effect of manufacturing the imaging system can beefficiently obtained.

Hereinafter, exemplary embodiments of the invention will be describedwith reference to the accompanying drawings. FIG. 1 is a block diagramshowing the schematic configuration of an imaging system and a methodfor manufacturing an imaging system according to an exemplary embodimentof the invention.

<Configuration of an Imaging System>

Hereinafter, the configuration of an imaging system will be described.

An imaging system 100 shown in FIG. 1 includes: an imaging lens 10; animaging device 20 which has a light receiving surface 21 on which aplurality of light receiving pixels are two-dimensionally arrayed andwhich images an optical image P1 of a subject projected onto the lightreceiving surface 21 through the imaging lens 10 and outputs first imagedata G1 expressing the subject; a coefficient storage unit 30 thatstores a restoration coefficient K corresponding to a blur state of thepoint image P1, indicated by the first image data G1 output from theimaging device 20, when the maximum diameter of an effective region ofthe point image projected onto the light receiving surface 21 throughthe imaging lens 10 is a size covering three or more pixels; and asignal processing unit 40 that executes restoration processing F on thefirst image data G1 using the restoration coefficient K stored in thecoefficient storage unit 30, the restoration processing F being executedto generate second image data G2 equivalent to the first image data G1output from the imaging device 20 when the resolving power of theimaging lens 10 is high.

The signal processing unit 40 executes the restoration processing F in acondition where a pixel region covering total nine or more pixelsincluding three or more pixels in a vertical direction and three or morepixels in a horizontal direction on the light receiving surface 21 isset as a minimum unit.

The imaging lens 10 has a first lens group, which includes at least onelens and has a positive power, and a second lens group, which includesat least one lens and in which a lens positioned closest to the imageside has a negative power, in order from the subject side (object side).

Here, the maximum diameter of the effective region of the point image P1projected onto the light receiving surface 21 is a diameter of theeffective region in a direction in which the effective region of thepoint image P1 projected onto the light receiving surface 21 includes alargest number of light receiving pixels.

In addition, a direction indicated by arrow Z in FIG. 1 is a directionof an optical axis of the imaging lens 10, and directions indicated byarrows X and Y are directions parallel to the light receiving surface21.

Here, a restoration coefficient acquisition apparatus 70A providedoutside the imaging system 100 acquires the restoration coefficient Kcorresponding to a blur state of the point image P1 expressed by thefirst image data G1 output from the imaging device 20 and makes therestoration coefficient K in the coefficient storage unit 30.

The restoration coefficient acquisition apparatus 70A includes: an idealpoint image storage unit 72 that stores data Dr, which is either designdata regarding a point image when there is no error in an optical systemincluding the imaging lens 10 or ideal point image state data regardingan ideal point image state exceeding it, beforehand; a point image blurstate acquisition unit 73 that analyzes a blur state of a point imageexpressed by the first image data G1 output from the imaging device 20and acquires blurred point image state data Db indicating the analysisresult; a point image diameter acquisition unit 74 that acquires themaximum diameter of an effective region of the point image P1 projectedonto the light receiving surface 21 through the imaging lens 10; adetermination unit 76 that determines whether or not the maximumdiameter obtained in the point image diameter acquisition unit 74 is asize covering three or more pixels on the light receiving surface 21;and a restoration coefficient acquisition unit 78A that is input withthe blurred point image state data Db output from the point image blurstate acquisition unit 73 and the data Dr which is design data or idealpoint image state data stored in the ideal point image storage unit 72,acquires coefficient data Dk indicating the restoration coefficient Kcorresponding to the blur state of the point image P1 expressed by thefirst image data G1 by an operation using both the blurred point imagestate data Db and the data Dr, and makes the restoration coefficient Kindicated by the coefficient data Dk stored in the coefficient storageunit 30 when the determination unit 76 determines that the maximumdiameter is a size covering three or more pixels on the light receivingsurface 21.

In addition, an imaging lens used in the imaging system of the inventionmay be adopted even if an optical image is “not focused” correctly on alight receiving surface through the imaging lens without being limitedto a case where the optical image is “focused” correctly on the lightreceiving surface necessarily through the imaging lens. Therefore, inthe invention, an explanation will be made assuming that an opticalimage is “projected” on a light receiving surface through an imaginglens. The state “not focused” is considered as a so-called blurredimage. For example, a state where a point image wider than an originalpoint image due to a manufacturing error is generated or a situationwhere only a point image a design value of which is larger than that ofa point image to be originally acquired due to design constraint (sizeor cost of an optical system) is also included.

In addition, the blurred point image state data Db mainly indicating adegradation state of the resolution of a point image as described abovemay be set to indicate the size of an effective region of the pointimage P1 or the brightness distribution (concentration distribution ofan image) on the light receiving surface of the point image P1, forexample.

<Operation of an Imaging System>

Next, an operation of the above imaging system will be described.

First, an example of a case where a restoration coefficient iscalculated by a restoration coefficient acquisition apparatus and therestoration coefficient is stored in a coefficient storage unit will bedescribed.

An optical image of a subject projected onto the light receiving surface21 through the imaging lens 10 is imaged by the imaging device 20, andthe first image data G1 indicating the subject output from the imagingdevice 20 are input to the point image blur state acquisition unit 73and the point image diameter acquisition unit 74.

The point image blur state acquisition unit 73 to which the first imagedata G1 is input analyzes a blur state of a point image expressed by thefirst image data G1 and outputs the analysis result to the blurred pointimage state data Db.

In addition, the point image diameter acquisition unit 74 to which thefirst image data G1 is input calculates the maximum diameter of theeffective region of the point image P1 projected onto the lightreceiving surface 21 and outputs diameter data Dm indicating the maximumdiameter. The determination unit 76 to which the diameter data Dmindicating the maximum diameter is input determines whether or not themaximum diameter of the effective region of the point image P1 is a sizecovering three or more pixels on the light receiving surface 21 andoutputs a signal Te when it is determined that the maximum diameter is asize covering three or more pixels.

The restoration coefficient acquisition unit 78A input with the signalTe is input with the blurred point image state data Db output from thepoint image blur state acquisition unit 73 and the data Dr which isdesign data or ideal point image state data stored beforehand in theideal point image storage unit 72, acquires the restoration coefficientK corresponding to the blur state of the point image P1 by an operationusing both the blurred point image state data Db and the data Dr, andoutputs the coefficient data Dk indicating the restoration coefficientK.

The coefficient data Dk output from the restoration coefficientacquisition unit 78A is input to the coefficient storage unit 30, suchthat the restoration coefficient K indicated by the coefficient data Dkis stored in the coefficient storage unit 30.

In addition, a DxO analyzer made by DxO Labs (France), which will bedescribed later, is mentioned as an example of realizing functions ofthe point image blur state acquisition unit 73 and point image diameteracquisition unit 74. In the DxO analyzer, a blur state (degradationstate of the resolution) of the point image P1 projected onto the lightreceiving surface 21 or the maximum diameter of the effective region maybe acquired by analyzing the first image data G1 output from the imagingdevice 20.

The restoration coefficient K is stored in the coefficient storage unit30 as described above, resulting in a state where the imaging system 100can execute restoration processing.

<Restoration Processing>

A case in which second image data that expresses an image with higherresolution than an image expressed by first image data is acquired byexecuting the restoration processing F on the first image data outputfrom the imaging device 20 using the restoration coefficient K stored inthe coefficient storage unit 30 will be described. Moreover, in thefollowing explanation, a case in which the restoration processing F ismainly performed on the first image data expressing a point image willbe described.

FIG. 2A is a view showing the light intensity distribution of a pointimage on the coordinates in which a vertical axis indicates a lightintensity E and a horizontal axis indicates an X-direction position on alight receiving surface. FIG. 2B is a view showing each pixel region(denoted by reference numeral Rg in the drawing) of a light receivingpixel, which forms a light receiving surface, and a point imageprojected onto the light receiving surface on the coordinates in which avertical axis indicates a Y-direction position on the light receivingsurface and a horizontal axis indicates an X-direction position on thelight receiving surface. FIG. 3A is a view showing an image of a pointimage displayed in an image expressed by the first image data, and FIG.3B is a view showing an image of a point image displayed in an imageexpressed by the second image data. In addition, the sizes of pixelregions (denoted by reference numeral Rg″ in the drawing) of the imagesshown in FIGS. 3A and 3B are equal. In addition, each pixel region Rg ofa light receiving pixel that forms the light receiving surface 21 andthe pixel region Rg″ of an image expressed by the first image data G1 orthe second image data G2 are regions corresponding to each other.

In addition, FIG. 4A is a view showing the light intensity distributionof a point image, which is to be projected onto the light receivingsurface 21 when the resolving power of the imaging lens 10 is high, onthe coordinates in which a vertical axis indicates the light intensity Eand a horizontal axis indicates the X-direction position on the lightreceiving surface. In addition, this may be regarded as indicating anideal point image state regardless of an optical system. FIG. 4B is aview showing each pixel region (denoted by reference numeral Rg in thedrawing) of a light receiving pixel, which forms the light receivingsurface, and a point image P2, which is to be projected onto the lightreceiving surface 21 when the resolving power of the imaging lens 10 ishigh, on the coordinates in which the vertical axis indicates theY-direction position on the light receiving surface and the horizontalaxis indicates the X-direction position on the light receiving surface.

A maximum diameter M1 of an effective region R1 of the point image P1which is an optical image projected onto the light receiving surface 21through the imaging lens 10 is a size covering three continuous pixelsof light receiving pixels that form the light receiving surface 21, asshown in FIG. 2B. In addition, the effective region R1 is a regioncovering total nine pixels including three pixels in the verticaldirection and three pixels in the horizontal direction on the lightreceiving surface 21. That is, the effective region R1 is a regionoccupying nine pixels (3 pixels×3 pixels) of light receiving pixels thatform the light receiving surface 21.

In addition, as shown in FIG. 2A, the effective region R1 of the pointimage P1 is a region having a light intensity of 1/e² or more of a peakintensity Ep1 on a light intensity distribution H1 indicating the pointimage P1.

The point image P1 projected onto the light receiving surface 21 isimaged by the imaging device 20, and the first image data G1 expressingthis point image P1 is output from the imaging device 20.

As shown in FIG. 3A, an image P1″ corresponding to the point image P1displayed in an image Zg1 indicated by the first image data G1 isdisplayed with an effective region R1″ of the image P1″ covering ninepixels (3 pixels×3 pixels) of the image with no change.

Then, the signal processing unit 40 to which the image data G1 is inputexecutes the restoration processing F on the first image data G1 using arestoration coefficient K1, obtaining the second image data G2.

As shown in FIGS. 3A and 3B, an effective region R2″ of an image P2″ ofa point image in an image Zg2 indicated by the second image data G2corresponding to the image P1″ of the point image expressed by the firstimage data G1 is smaller than the effective region R1″ of the image P1″of the point image in the image Zg1 indicated by the first image dataG1. Accordingly, a maximum diameter M2″ (region corresponding to threepixels of the pixel region Rg″) of the image P2″ of the point imagedisplayed in the image Zg2 becomes also smaller than a maximum diameterM1″ (region corresponding to one pixel of the pixel region Rg″) of theimage P1″ of the point image displayed in the image Zg1.

That is, the image P2″ of the point image expressed by the second imagedata G2 shown in FIG. 3B and an image of a point image expressed by thefirst image data output from the imaging device 20 which has imaged thepoint image P2 (refer to FIG. 4) to be projected onto the lightreceiving surface 21 when the resolving power of the imaging lens 10 ishigh become equal images.

More specifically, the image P2″ (refer to FIG. 3B) of the point imageexpressed by the second image data G2 obtained by executing therestoration processing F on the first image data G1, which is outputfrom the imaging device 20 that has imaged the point image P1 (refer toFIGS. 2A and 2B) which is projected onto the light receiving surface 21through the imaging lens 10 and whose effective region R1 covers ninepixels, using the restoration coefficient K and an image of a pointimage expressed by the first image data G1 output from the imagingdevice 20 which has imaged the point image P2 (the maximum diameter M2of the effective region R2 is included in one pixel region Rg; refer toFIGS. 4A and 4B), which is expected to be projected onto the lightreceiving surface 21 when the resolving power of the imaging lens 10 ishigh, are equal images.

In addition, the effective region R2 of the point image P2 included inone pixel region Rg on the light receiving surface 21 shown in FIGS. 4Aand 4B is a region having a light intensity of 1/e² or more of a peakintensity Ep2 on a light intensity distribution H2 indicating the pointimage P2, similar to the case of the point image P1. Here, the effectiveregion R2 of the point image P2 has a size included in one pixel regionRg.

Thus, the resolution of an image expressed by the second image dataobtained by performing restoration processing on the first image datamay be higher than that of the image expressed by the first image data.

In addition, since the same image as an image obtained when the depth offield of the imaging lens 10 is made large can be obtained by therestoration processing F, it can be said that the restoration processingmakes the depth of field of the imaging lens 10 substantially large.

For example, image restoration processing disclosed in paragraphs([0002] to [0016]) of JP-A-2000-123168 may be adopted as the restorationprocessing F of the signal processing unit 40 using the restorationcoefficient K corresponding to a state of the point image P1 expressedby the first image data G1.

Although a case of imaging a point image has been described, an opticalimage of a subject projected onto the light receiving surface 21 throughthe imaging lens 10 is regarded as a group of point images expressingthe subject. Therefore, even if any subject is imaged, the second imagedata expressing an image can be generated with resolution higher thanthe image expressed by the first image data by performing restorationprocessing on the first image data.

<Modification of a Restoration Coefficient Acquisition Apparatus>

Hereinafter, a modification of the restoration coefficient acquisitionapparatus will be described.

The restoration coefficient acquisition apparatus which makes therestoration coefficient K1, which corresponds to a blur state of a pointimage expressed by the first image data output from the imaging device,stored in the coefficient storage unit 30 may be constructed like arestoration coefficient acquisition apparatus 70B of a second example ora restoration coefficient acquisition apparatus 70C of a third example,which will be described below and is different from the restorationcoefficient acquisition apparatus 70A in the first example.

FIG. 5 is a view showing the restoration coefficient acquisitionapparatus 70B of the second example, and FIG. 6 is a view showing therestoration coefficient acquisition apparatus 70C of the third example.FIG. 7 is a view showing an imaging system including a restorationcoefficient acquisition apparatus, and FIG. 8 is a view showing animaging system including a signal processing unit that has a restorationcoefficient acquisition apparatus and a coefficient storage unit.Moreover, in FIGS. 5 to 8, constituent components having the samefunctions as the restoration coefficient acquisition apparatus 70A ofthe first example are denoted by the same reference numerals as in thecase of the restoration coefficient acquisition apparatus 70A of thefirst example.

As shown in FIG. 5, the restoration coefficient acquisition apparatus70B of the second example includes: a candidate coefficient storage unit79 that stores candidates K1, K2, . . . of each restoration coefficientcorresponding to each of blur states of point images classified into aplurality of types beforehand; a point image blur state acquisition unit73 that analyzes a blur state of a point image expressed by the firstimage data G1 output from the imaging device 20, acquires blurred pointimage state data Db indicating the analysis result, and outputs theblurred point image state data Db to a restoration coefficientacquisition unit 78B to be described later; a point image diameteracquisition unit 74 that acquires the maximum diameter of an effectiveregion of the point image P1 projected onto the light receiving surface21 through the imaging lens 10; a determination unit 76 that determineswhether or not the maximum diameter obtained in the point image diameteracquisition unit 74 is a size covering three or more pixels on the lightreceiving surface 21; and the restoration coefficient acquisition unit78B that selects a restoration coefficient (for example, K1), whichcorresponds to a blur state of the point image P1 expressed by theblurred point image state data Db, among the restoration coefficientcandidates K1, K2, . . . and makes the restoration coefficient K1 storedin the coefficient storage unit 30 when the determination unit 76determines that the maximum diameter is a size covering three or morepixels on the light receiving surface 21.

In the restoration coefficient acquisition apparatus 70B, the pointimage diameter acquisition unit 74 acquires the maximum diameter of theeffective region of the point image P1 projected onto the lightreceiving surface 21 through the imaging lens 10 and outputs diameterdata Dm indicating the maximum diameter to the determination unit 76.The determination unit 76 to which the diameter data Dm is inputdetermines whether or not the maximum diameter is a size covering threeor more pixels on the light receiving surface 21 and outputs a signalTe, which indicates that the maximum diameter is a size covering threeor more pixels, to the restoration coefficient acquisition unit 78B whenit is determined that the maximum diameter is a size covering three ormore pixels. The restoration coefficient acquisition unit 78B to whichthe signal Te is input selects a restoration coefficient (for example,K1), which corresponds to a blur state of the point image P1 expressedby the blurred point image state data Db, among the restorationcoefficient candidates K1, K2, . . . stored in the candidate coefficientstorage unit 79 and outputs coefficient data Dk indicating therestoration coefficient K1 to the coefficient storage unit 30 such thatthe coefficient data Dk is stored in the coefficient storage unit 30.

That is, a restoration coefficient (for example, K1) selectedcorresponding to a blur state of a point image expressed by the firstimage data G1 among the candidates K1, K2, . . . of each restorationcoefficient corresponding to each of blur states of point imagesclassified into a plurality of types is stored in the coefficientstorage unit 30.

On the other hand, as shown in FIG. 6, the restoration coefficientacquisition apparatus 70C of the third example includes: a candidatecoefficient storage unit 79 that stores candidates K1, K2, . . . of eachrestoration coefficient corresponding to each of blur states of pointimages classified into a plurality of types beforehand; an ideal pointimage storage unit 72 that stores data Dr, which is either ideal pointimage state data or design data regarding an ideal point image projectedonto the light receiving surface 21 through an imaging lens with highresolving power, beforehand when the resolving power of the imaging lens10 is high; a point image blur state acquisition unit 73 that analyzes ablur state of a point image expressed by the first image data G1 outputfrom the imaging device 20, acquires blurred point image state data Dbindicating the analysis result, and outputs the blurred point imagestate data Db to a restoration coefficient acquisition unit 78C to bedescribed later; a point image diameter acquisition unit 74 thatacquires the maximum diameter of an effective region of the point imageP1 projected onto the light receiving surface 21 through the imaginglens 10; and a determination unit 76 that determines whether or not themaximum diameter obtained in the point image diameter acquisition unit74 is a size covering three or more pixels on the light receivingsurface 21.

In addition, the restoration coefficient acquisition apparatus 70Cincludes the restoration coefficient acquisition unit 78C that selects arestoration coefficient (for example, K1), which corresponds to a blurstate of the point image P1 expressed by the blurred point image statedata Db output from the point image blur state acquisition unit 73,among the restoration coefficient candidates K1, K2, . . . , acquirescoefficient data Dk (K1″) indicating a correction-completed restorationcoefficient K1″ obtained by collecting the restoration coefficient K1 byan operation using the blurred point image state data Db and the data Drwhich is ideal point image state data or design data of a point imagestored beforehand in the ideal point image storage unit 72, and makesthe correction-completed restoration coefficient K1″ indicated by thecoefficient data Dk (K1″) stored in the coefficient storage unit 30 whenthe determination unit 76 determines that the maximum diameter is a sizecovering three or more pixels on the light receiving surface 21.

In the restoration coefficient acquisition apparatus 70C, the pointimage diameter acquisition unit 74 acquires the maximum diameter of theeffective region of the point image P1 projected onto the lightreceiving surface 21 through the imaging lens 10 and outputs diameterdata Dm indicating the maximum diameter to the determination unit 76.The determination unit 76 to which the diameter data Dm is inputdetermines whether or not the maximum diameter is a size covering threeor more pixels on the light receiving surface 21 and outputs a signalTe, which indicates that the maximum diameter is a size covering threeor more pixels, to the restoration coefficient acquisition unit 78B whenit is determined that the maximum diameter is a size covering three ormore pixels. The restoration coefficient acquisition unit 78B to whichthe signal Te is input selects a restoration coefficient (for example,K1), which corresponds to a blur state of the point image P1 expressedby the blurred point image state data Db, among the restorationcoefficient candidates K1, K2, . . . stored in the candidate coefficientstorage unit 79, acquires correction-completed restoration coefficientK1″ obtained by further correcting the restoration coefficient K1 by anoperation using the blurred point image state data Db and the data Drwhich is ideal point image state data or design data of a point imagestored beforehand in the ideal point image storage unit 72, and makesthe correction-completed restoration coefficient K1″ stored in thecoefficient storage unit 30.

That is, the correction-completed restoration coefficient K1″ obtainedby further correcting a restoration coefficient (for example, K1), whichis selected corresponding to a blur state of the point image P1expressed by the first image data G1 among a plurality of types ofrestoration coefficient candidates corresponding to each of blur statesof point images classified into a plurality of types, according to theblur state of the point image is stored in the coefficient storage unit30.

In addition, the imaging system 100 may include the restorationcoefficient acquisition apparatus 70A, 70B, or 70C as a part thereof ormay not include any of the restoration coefficient acquisitionapparatuses 70A, 70B, and 70C.

In addition, an imaging system 100′ shown in FIG. 7 includes arestoration coefficient acquisition apparatus 70, which has the samefunction as the restoration coefficient acquisition apparatus 70A, 70B,or 70C, provided in a housing of the imaging system. The imaging systemmay be constructed in this way.

In addition, an imaging system 100″ shown in FIG. 8 includes theabove-described restoration coefficient acquisition apparatus 70 andcoefficient storage unit 30 provided in a signal processing unit 40″.The imaging system may be constructed in this way.

<Performance of an Imaging System>

Next, performance of an imaging system configured to include the imaginglens 10 and the imaging device 20, which are used in the above imagingsystem 100, will be described.

FIG. 9 is a view schematically showing a change in a maximum diameter ofan effective region of a point image, which corresponds to an objectpoint and is projected onto a light receiving surface when the objectpoint is made to move in an optical-axis direction, on the coordinatesin which a horizontal axis indicates an optical-axis-direction distanceU from an imaging lens to the object point on a logarithmic scale (m)and a vertical direction indicates a length corresponding to the number(N) of pixel regions located continuously on a light receiving surface.

Here, an object point was moved from a position of a near pointapproximately adjacent to an imaging lens (position adjacent to theimaging lens by about 0.01 m) to a position of a far point approximatelyinfinitely distant from the imaging lens (position distant from theimaging lens by about 10 m).

Three kinds of curves (solid lines) indicated by groups A-1, A-2, andA-3 in FIG. 9 schematically show changes in maximum diameters ofeffective regions of point images projected onto different specificregions on the light receiving surface 21 through the imaging lens 10 ofthe imaging system of the invention (specific regions on the lightreceiving surface having different image heights). In addition, a curvedline (dotted line) indicated by a group Aw in FIG. 9 shows a typicalchange in a maximum diameter of an effective region of a point imageprojected onto the light receiving surface through an imaging lens usedin a known imaging system (for example, an onboard camera, the camerafor cellular phones, a portable cellular phone camera, or a camera formedical apparatus).

As can be seen from FIG. 9, the maximum diameter of an effective regionof a point image obtained by projecting an object point onto the lightreceiving surface 21 largely changes from a size corresponding to onepixel to a size corresponding to thirty pixels according to the movementof the object point in the optical-axis direction.

On the other hand, the maximum diameter of the effective region of thepoint image obtained by projecting the object point onto the lightreceiving surface 21 through the imaging lens 10 provided in the imagingsystem 100 of the invention is a size covering three or more pixels andten pixels or less in all cases of the groups A-1, A-2, and A-3. Thatis, there is little fluctuation in the size of the effective region ofthe point image on the light receiving surface regardless of thedistance from the imaging lens 10 to the object point and the position(for example, an image height on the light receiving surface) of theprojected point image on the light receiving surface. In addition, alsoin a point image projected from any position of X, Y, and Z directionsonto the light receiving surface through the imaging lens 10, it can besaid that a fluctuation in the size of the effective region of the pointimage is small.

FIG. 10 is a view schematically showing a change in a value (%) of MTFcharacteristics regarding an optical image of an object point projectedonto a light receiving surface when the object point is made to move inan optical-axis direction, on the coordinates in which a horizontal axisindicates an optical-axis-direction distance U from an imaging lens tothe object point on a logarithmic scale (m) and a vertical directionindicates the value (%) of MTF characteristics.

Here, an object point was moved from a position of a near pointapproximately adjacent to an imaging lens position adjacent to theimaging lens by about 0.01 m) to a position of a far point approximatelyinfinitely distant from the imaging lens (position distant from theimaging lens by about 10 m).

Three kinds of curves (solid lines) regarding the imaging system of theinvention indicated by groups B-1, B-2, and B-3 in FIG. 10 schematicallyshow a value (%) of MTF characteristics regarding optical imagesprojected onto different specific regions on the light receiving surfacethrough the imaging lens 10 (specific regions having different imageheights). In addition, a curved line (dotted line) indicated by a groupBw in FIG. 10 shows a typical change in a value (%) of MTFcharacteristics regarding an optical image projected onto a lightreceiving surface in a known imaging system.

As can be seen from FIG. 10, in a known imaging system, a value (%) ofMTF characteristics regarding an optical image projected onto the lightreceiving surface 21 largely changes from 0% to a value exceeding 80%.In addition, false resolution occurs at an object point located in aregion (region at which a value of MTF characteristics is turned up from0%), which is closer to the imaging lens 10 than a position at which avalue of MTF characteristics becomes 0%, of a near point where theimaging lens 10 and the object point are adjacent to each other. Inaddition, the false resolution also occurs at an object point located ina region (region at which a value of MTF characteristics is turned upfrom 0%), which is more distant than a position at which a value of MTFcharacteristics becomes 0%, of a far point where the imaging lens 10 andthe object point are distant from each other.

On the other hand, the value of MTF characteristics regarding an opticalimage projected onto the light receiving surface 21 through the imaginglens 10 provided in the imaging system 100 of the invention is a size of10% or more and 60% or less in any case of the groups B-1, B-2, and B-3,and the false resolution does not occur. That is, a fluctuation in avalue of MTF characteristics regarding an optical image projected onto alight receiving surface is small and the false resolution does not occurregardless of the distance from the imaging lens 10 to an object pointand the position (image height) on the light receiving surface of theprojected optical image. In addition, it can be said that a fluctuationin the value of the MTF characteristics regarding an optical imageprojected from any position of X, Y, and Z directions, that is, anyposition in a three-dimensional space onto the light receiving surfacethrough the imaging lens 10 is also small.

As described above, according to the imaging system of the invention,when the resolution of an image expressed by first image data outputfrom an imaging system does not reach an intended level, it is notnecessary to specify the cause and readjust or reassemble the imaginglens unlike the related art. That is, second image data that expressesan image having an intended resolution can be obtained only by storing arestoration coefficient corresponding to a blur state of a point imagein a coefficient storage unit and performing restoration processing onthe first image data. As a result, the quality of image data obtained byimaging an optical image projected onto the light receiving surface canbe easily improved. In addition, it can be said that lack of theresolving power in an imaging system can be recovered easily.

<Method of Manufacturing an Imaging System>

Hereinafter, a method of manufacturing the imaging system of theinvention, that is, a method of manufacturing arestoration-coefficient-storage-completed imaging system in whichstorage of a restoration coefficient is completed by storing an intendedrestoration coefficient in an imaging system in which the intendedrestoration coefficient is not stored will be described with referenceto FIGS. 1, 5, and 6.

In the method of manufacturing an imaging system,restoration-coefficient-storage-completed imaging systems 100A, 100B, .. . capable of executing restoration processing by storing a restorationcoefficient in the coefficient storage unit 30 is manufactured.

In addition, the imaging systems 100A, 100B, . . . are equal to theimaging system 100 already described with reference to FIGS. 1 to 10.

The method of manufacturing an imaging system is a method ofmanufacturing the imaging systems 100A, 100B, . . . each of whichexecutes restoration processing by using the restoration coefficient Kstored in the coefficient storage unit 30 and includes: the imaging lens10; the imaging device 20 which has the light receiving surface 21 onwhich a plurality of light receiving pixels are arrayed in atwo-dimensional manner and which images an optical image of a subjectprojected onto the light receiving surface 21 through the imaging lens10 and outputs the first image data G1 expressing the subject; thesignal processing unit 40 that executes the restoration processing F onthe first image data G1 in a condition where a pixel region coveringtotal nine pixels including three or more pixels in the verticaldirection and three or more pixels in the horizontal direction on thelight receiving surface 21 is set as a minimum unit, the restorationprocessing F being executed to generate the second image data G2equivalent to the first image data G1 output from the imaging device 20when the resolving power of the imaging lens 10 is high; and thecoefficient storage unit 30 that stores the restoration coefficient Kused in the restoration coefficient.

In this manufacturing method, the point image P1 is projected onto thelight receiving surface 21 through the imaging lens 10 and therestoration coefficient K corresponding to a state of the point image P1expressed by the first image data G1 output from the imaging device 20is stored in the coefficient storage unit 30.

In the method of manufacturing an imaging system, a method of obtaininga restoration coefficient using the restoration coefficient acquisitionapparatus 70A of the first example, the restoration coefficientacquisition apparatus 70B of the second example, or the restorationcoefficient acquisition apparatus 70C of the third example and storingthe restoration coefficient in a coefficient storage unit of each of theimaging systems 100A, 100B, . . . .

Hereinafter, methods of manufacturing imaging systems using therestoration coefficient acquisition apparatus 70A of the first example,the restoration coefficient acquisition apparatus 70B of the secondexample, and the restoration coefficient acquisition apparatus 70C ofthe third example will be specifically described. In addition, sinceconfigurations and operations of the imaging systems 100A, 100B, . . . ,restoration coefficient acquisition apparatus 70A of the first example,restoration coefficient acquisition apparatus 70B of the second example,and restoration coefficient acquisition apparatus C of the third exampleare similar to those in the imaging system 100, a repeated explanationwill be omitted. Accordingly, a method of manufacturing an imagingsystem not overlapping the explanation on the imaging system 100 will bedescribed.

<Method of Manufacturing an Imaging System Corresponding to theRestoration Coefficient Acquisition Apparatus 70A of the First Example>

In a manufacturing process of “1 to 1” correspondence for storing arestoration coefficient, which is individually calculated for everyimaging system, in each imaging system, the following processes areneeded.

(1) Point image measurement and determination on uniformity within ascreen

(2) Extraction of a coefficient group (restoration coefficient) applyingoptimal restoration processing

(3) Recording of an optimal coefficient group. Each of the functionswill be described in more detail

The process (1) is a function of actually measuring and determining animaging ability (resolving power) in the combination of each imaginglens and an imaging device. As a means for measuring an optical pointimage on the basis of an electric signal (first image data) obtainedfrom an imaging device, a DxO analyzer made by DxO Co. in France iscommercially available. This uses a concept of expressing blur calledB×U that the DxO Co. proposes, which allows to obtain a point image(both an optical point image and a point image after image processing)from an output signal from a digital camera.

Specifically, the DxO analyzer calculates the point image size at anarbitrary point on a light receiving surface of an imaging device byanalyzing image data (first image data) obtained by taking an intendeddesignated chart (chart in which a number of black dots are arrayed onwhite paper) (http://www.dxo.com/jp/image_quality/dxo_analyzer).

In addition, any means for measuring an optical point image may be usedas long as the means can calculate a point image from an output signalfrom a digital camera (that is, a sensor).

On the other hand, the size of a point image corresponding to an opticaldesign value can be calculated with a tool which designed the opticalsystem. Accordingly, by comparing the size of a “design value pointimage” obtained in the calculation with the size of a “measured pointimage” measured in a measuring apparatus, such as the DxO analyzer, itcan be determined how far the measured point image deviates from thedesign value. For example, in many cases, the size of the measured pointimage when there is an assembly error in an optical component becomeslarger than the design value. In addition, the shape or brightnessdistribution of an effective region of a point image projected onto alight receiving surface of an imaging device is originally symmetricalwith respect to a point. However, when the imaging lens is inclined orthe axis deviates, front blur and back blur, a so-called “single-sidedblur state” partially occurs in the shape or the brightnessdistribution. Such deviation from a design value is calculated bycomparing the “design value point image” with the “measured pointimage”, such that a determination on whether or not it can be said asthe design value may be further made. In addition, even if attention isnot made to the design value point image, it is also possible to definean ideal state arbitrarily, compare the ideal state (“ideal pointimage”) with a “measured point image”, and determine the difference.

The process (2) is a step of executing restoration processing based on akernel Wiener filter and obtaining a coefficient group (restorationcoefficient) for making the “measured point image” similar to the“design value point image” or the “ideal point image” by calculation.The Kernel Wiener filter is widely used in a technique of estimating anoriginal signal from an observed signal included in a noise when theoriginal signal is observed together with the noise through intendedfiltering, as disclosed in the document “title “Kernel Wiener Filter”,Yoshikazu Washizawa and Yukihiko Yamashita, 2003 Workshop onInformation-Based Induction Sciences, (IBIS2003), Kyoto, Japan, Nov.11-12, 2003”. Here, assuming that the original signal is a “takenobject”, the filtering is “imaging lens+imaging device”, the observedsignal is an “image signal (first image data)”, and the noise is a“difference between a design value point image (or an ideal point image)and a measured point image”, the “taken object” can be estimated byapplication of the kernel Wiener filter.

If there is no error factor in the “imaging lens+imaging device” of anactual object, a taken object becomes an image signal and an ideal“image signal (second image data)” is theoretically acquired after therestoration processing. Practically, there is a measurement error in theprocess (1) and a noise component partially remains without beingcompletely removed. However, it is clear that a measured point imagebecomes similar to a design value point image or an ideal point image,and the quality of a final image is improved.

Specifically, even if an optical point image is larger than a designvalue or is not uniform on an imaging surface due to a certain errorfactor, performance allowable in practical use can be secured by makingthe point image uniform on the imaging surface or correcting the pointimage small by restoration processing. In addition, even in an opticalsystem which is constructed not to avoid low performance (optical pointimage is large compared with an element pitch) in terms of design aswell as an error factor in manufacture, the optical performance can beseemingly improved by correcting the point image. By pursuing animprovement in optical performance in appearance, it becomes possible toexceed the critical resolution theoretically indicated. This is veryuseful in considering the tendency of miniaturization of a pixel size inrecent years.

Here, the critical resolution is set as a size of the Airy disk, and aradius Re of an effective region (peak intensity×(1/e²)) of a pointimage intensity of an aplanatic lens and a radius Re making theintensity zero are defined by the following expressions. Pixel pitchesof latest CMOS devices used as imaging devices are 2.2 microns and 1.75microns, and it is expected that 1.4 microns and 1.0 microns will be themainstream from now on. As an example, Re and Re are calculated asfollows in the case of F2.8 and a wavelength of 550 nm.

Re (radius of an effective region of a point image intensity)=0.82λF=0.82×2.8×550×0.001=1.26 microns (diameter of the effective region ofthe point image intensity 2.52 microns)

Rc (radius making the point image intensity zero)=1.22λF=1.22×2.8×550×0.001=1.88 microns (diameter making the point imageintensity zero=3.76 microns).

In this case, the pixel pitch is already over the diffraction limited.

Although non-aberration is assumed in the diffraction limited, thenon-aberration is not realized in an actual optical system. Particularlywhen requests of miniaturization and reduction in cost are considered,the aberration remains rather and accordingly, the compromisedperformance cannot be avoided. The restoration processing using thekernel Wiener filter can improve the quality of a final image up to apractical degree in such a situation.

Although it is assumed that the restoration processing is executed on aspecific image surface or at the extreme vicinity (range of front blurand back blur), it is also possible to extend the focal depth ifrestoration processing for eliminating a difference between a measuredpoint image and a design value point image in a number of image surfacegroups in the defocusing direction corresponding to a fluctuation intaking distance is considered.

Regarding execution of the restoration processing, it is desirable toperform optimal restoration processing for every combination of “imaginglens+imaging device” since a noise component to be removed variesaccording to each “imaging lens+imaging device”. In this case,preferably, the algorithm of restoration processing itself is equal anda “coefficient group” referred herein is optimal.

The process (3) is a step of actually combining the “optimal coefficientgroup” with a set of “imaging lens+imaging device”. In order to do so,it is necessary to store a coefficient group for executing the optimalrestoration processing in an intended recording medium and to add thecoefficient group to the set of “imaging lens+imaging device”.Accordingly, a recording process is required.

An optical point image is corrected in a form suitable for theapplication by using an imaging system as a set of “imaging lens+imagingdevice+recording medium”, and an image with satisfactory quality can beobtained eventually. Specifically, even if the resolving power is notsatisfactory for a certain reason (manufacturing tolerance and originaldesign value are low), a means capable of obtaining satisfactoryresolving power as an image after processing is provided. In addition, afocal depth magnifying means suitable for the characteristics of eachset of imaging lens and imaging device may also be provided.

<Method of Manufacturing an Imaging System Corresponding to theRestoration Coefficient Acquisition Apparatus 70B of the Second Example>

A second preferred method of manufacturing the point image correctionoptical system configured to include an imaging lens, an imaging device,and a signal processing circuit will be described. Here, a case ofmanufacturing a large number of digital cameras at low cost is assumed.In the manufacturing process, (1) building of a library of a coefficient(restoration coefficient) group used in restoration processing, (2)point image measurement and determination on uniformity within a screen,(3) extraction of a coefficient group allowing optimal restorationprocessing in the unit of a group from the library, and (4) recording ofan optimal coefficient group in the unit of a group are needed. Each ofthe functions will be described in more detail.

In the process (1), an intended number of imaging lenses (for example,1/10 of all lots) enough to show the overall tendency are measuredbeforehand and resolution tendencies (malfunction tendencies) aredivided into groups. Optimal restoration processing is performed on eachof the groups and an optimal coefficient group in the unit of each groupis acquired, thereby building a library. Although it is ideal to apply acoefficient group in the “1 to 1” correspondence like the first example,this is not suitable for a case of mass production or a case where costreduction is needed. Therefore, the library in which the entire part isdivided into intended groups and optimal solution is calculated in thegroup unit is created, like this example.

Although the process (2) is the same as the process (1) in the firstexample, it is determined that a measured point image will belong towhich of the groups acquired in the process (1) in the second example.Practically, for imaging lenses other than the imaging lenses measuredat the time of group division, application to a group is also made (forexample, 9/10 of all lots).

The process (3) is a step of extracting an optimal coefficient group ofthe group determined in the process (2) from the library, and theselected coefficient group is applied to the set of “imaginglens+imaging device”. In this case, an optimal coefficient group foreach set of “imaging lens+imaging device” is not acquired fully. Sincethis shortens the operation time required in the first example, massproduction can be realized at low price.

The process (4) is the same as the process (3) in the first example.

<Method of Manufacturing an Imaging System Corresponding to theRestoration Coefficient Acquisition Apparatus 70C of the Third Example>

A third preferred method of manufacturing the point image correctionoptical system configured to include an imaging lens, an imaging device,and a signal processing circuit will be described. Here, a case ofmanufacturing a large number of digital cameras at low cost is assumed.In the manufacturing process, (1) building of a library of a coefficient(restoration coefficient) group used in restoration processing, (2)point image measurement and determination on uniformity within a screen,(3) extraction of a coefficient group allowing optimal restorationprocessing from the library, (4) partial modification of thecorresponding coefficient group, and (5) recording of the modifiedcoefficient group are needed. Each of the functions will be described inmore detail.

The processes (1), (2), and (3) are the same as the processes (1), (2),and (3) in the second example.

The process (4) is a process of partially modifying the coefficientgroup extracted. Although the coefficient group is an arrangement ofcertain numbers, a modification needed for certain “imaging lens+imagingdevice” is made by correcting only a part thereof. Since coefficientsare partially modified unlike the first example in all coefficientgroups are optimized, the modification is completed in a short time.

The process (5) is a step of recording the corrected coefficient groupthat has been modified, and a set of “imaging lens+imagingdevice+recording medium” is thus formed.

Thus, the imaging system manufactured by using the method ofmanufacturing an imaging system of the invention can easily improve thequality of image data obtained by imaging an optical image projectedonto a light receiving surface.

<Modification of Each Constituent Element>

Hereinafter, modifications of constituent elements in the imaging systemand the method of manufacturing an imaging system will be described.

In addition, the signal processing unit may execute the restorationprocessing with a pixel region, which includes the whole effectiveregion but is not the minimum, as a minimum unit without being limitedto a case where the restoration processing is executed in a conditionwhere a minimum pixel region including the entire effective region of apoint image projected onto a light receiving surface is set as a minimumunit.

Furthermore, the signal processing unit may execute the restorationprocessing such that the size of an effective region of a point image inan image expressed by first image data is equal to or larger than thesize of an effective region of a point image in an image expressed bysecond image data without being limited to a case where the restorationprocessing is executed such that the size of the effective region of thepoint image in the image expressed by the second image data is smallerthan the size of the effective region of the point image in the imageexpressed by the first image data.

Moreover, in apparatuses requested to have a large depth of field, suchas an imaging apparatus, a portable terminal apparatus, an onboardapparatus, and a medical apparatus of the invention including theabove-described imaging system, the quality of image data obtained byimaging an optical image projected onto the light receiving surface ofthe imaging system provided in each apparatus can be easily improved asdescribed above.

FIG. 22 is a view showing an automobile in which an onboard apparatusincluding an imaging system is mounted.

As shown in FIG. 11, onboard apparatuses 502 to 504 each including theimaging system of the invention may be used in a state mounted in anautomobile 501 and the like. The automobile 501 includes: the onboardapparatus 502 which is a camera provided outside the vehicle in order toimage a blind zone of a side surface on a front passenger side; theonboard apparatus 503 which is a camera provided outside the vehicle inorder to image a blind zone on a rear side of the automobile 501; andthe onboard apparatus 504 which is a camera attached to a back surfaceof a room mirror and provided inside the vehicle in order to image thesame viewing field range as a driver.

FIG. 23 is a view showing a portable cellular phone which is a portableterminal apparatus including an imaging system.

As shown in the drawing, a portable cellular phone 510 has an imagingsystem 512 provided in a housing 511 of the portable cellular phone.

FIG. 24 is a view showing an endoscope apparatus which is a medicalapparatus including an imaging system.

As shown in the drawing, an endoscope apparatus 520 that observes abiological tissue 525 has an imaging system 522, which is used to imagethe biological tissue 525 illuminated by illumination light La, providedon a front end 521 of the endoscope apparatus 520.

Thus, in the imaging apparatus, the portable terminal apparatus, theonboard apparatus, and the medical apparatus of the invention includingthe above-described imaging system, a known imaging system provided inan imaging apparatus, a portable terminal apparatus, an onboardapparatus, and a medical apparatus known from the past may be easilyreplaced. That is, the imaging apparatus, the portable terminalapparatus, the onboard apparatus, and the medical apparatus of theinvention may be constructed by replacing the known imaging systemsprovided in the known apparatuses with the imaging system of theinvention without changing the apparatus size, shape, and the like ofthe imaging apparatus, portable terminal apparatus, onboard apparatus,and medical apparatus known from the past.

In addition, in the imaging system of the invention, the imaging lensand the imaging device may be constructed such that the maximum diameterof an effective region of a point image, which is projected onto a lightreceiving surface from any position of X, Y, and Z directions of anobject space within a range which is restricted to, for example, 10 f ormore in the Z direction and is restricted up to an object height in theX and Y directions, becomes a size covering three or more pixels oflight receiving pixels which form the light receiving surface of theimaging device.

In addition, the imaging lens is preferably constructed such that avalue of MTF characteristics of an optical image of a subject, which isprojected onto a light receiving surface through the imaging lens fromany position of X, Y, and Z directions distant ten times or more of afocal length of the imaging lens, is a positive value. In addition, the“position distant ten times or more of a focal length of an imaginglens” means a “position distant ten times or more of the focal lengthtoward the subject along the optical-axis direction (Z-axis direction)of the imaging lens from a reference position when a position, at whichone of lens surfaces forming the imaging lens closest to the subjectside and the optical axis of the imaging lens cross each other, is setas the reference position”.

In addition, the imaging system of the invention may also be constructedsuch that the maximum diameter of an effective region only in a pointimage, which is projected onto a light receiving surface through animaging lens from a position at which the imaging lens and the imagingdevice are limited in at least one of the X, Y, and Z directions,becomes a size covering three or more pixels of light receiving pixelswhich form the light receiving surface. In such a case, the second imagedata may be obtained by executing the restoration processing only on thefirst image data indicate a region where the maximum diameter of aneffective region of a point image projected onto the light receivingsurface is a size covering three or more pixels of light receivingpixels.

Furthermore, the imaging system may be constructed such that an opticalimage of a subject is projected onto a light receiving surface onlythrough an optical member having an axisymmetric shape or the opticalimage of the subject is projected onto the light receiving surfacethrough an optical member having a non-axisymmetric shape. In addition,it is preferable that the imaging lens have a large depth of field. Thatis, it is preferable to construct the imaging lens and the imagingdevice such that a change in a blur state of a point image projectedonto a light receiving surface is decreased even if a change in a statewhere an optical image of a subject is projected onto the lightreceiving surface occurs due to the movement of the subject or focusadjustment of the imaging lens, for example. More specifically, it ispreferable to construct the imaging lens and the imaging device suchthat changes in size and contrast of the effective region of the pointimage projected onto the light receiving surface are decreased. However,the imaging system may also be made to include an imaging lens having asmall depth of field without being limited to a case in which theimaging system includes an imaging lens having a large depth of field.

In addition, the imaging device used in the above-described imagingsystem may be a CCD device or a CMOS device.

<Lens Configuration and Operation of an Imaging Lens>

Next, configuration and operation of an imaging system in each of firstto third examples used in the above imaging system 100 will be describedin detail. Imaging lenses 10A to 10C, which will be described later,used in imaging systems of the first to third examples become examplesof the above-described imaging lens 10.

In addition, the imaging lens 10 has a first lens group, which includesat least one lens and has a positive power, and a second lens group,which includes at least one lens and in which a lens positioned closestto an image side has a negative power, in order from a subject side(object side).

<Regarding an Imaging System of Example 1>

FIG. 11 is a cross-sectional view showing the schematic configuration ofan imaging lens 10A including four single lenses in Example 1. FIGS. 12Ato 12D are views showing a change in a value (%) of MTF characteristicsof an optical image projected onto a light receiving surface when thelight receiving surface is defocused with respect to the imaging lensonto the coordinates in which the horizontal axis indicates a defocusamount Ud (μm) in the optical-axis direction (Z-axis direction) of thelight receiving surface onto which an image of a subject is projectedthrough the imaging lens 10A and the vertical axis indicates the value(%) of MTF characteristics. Here, a defocus range of the light receivingsurface 21A is 400 μm.

More specifically, FIGS. 12A to 12D are views showing a change in thevalue (%) of MTF characteristics regarding optical images projected atvarious image heights when the light receiving surface 21A is defocusedin a state where the position of the subject with respect to the imaginglens 10A is fixed. FIG. 12A shows a change in a value of MTFcharacteristics in a spatial frequency of 20 line/mm, FIG. 12B shows achange in a value of MTF characteristics in a spatial frequency of 30line/mm, FIG. 12C shows a change in a value of MTF characteristics in aspatial frequency of 40 line/mm, and FIG. 12D shows a change in a valueof MTF characteristics in a spatial frequency of 50 line/mm.

In addition, for a horizontal axis Ud indicating the defocus amountshown in FIGS. 12A to 12D, a direction (direction in which a value of Udapproaches 400 μm) in which the value increases indicates a direction inwhich the imaging lens and the light receiving surface become distantfrom each other and a direction (direction in which the value of Udapproaches 0) in which the value decreases indicates a direction inwhich the imaging lens and the light receiving surface become close toeach other.

As shown in FIG. 11, the imaging lens 10A has an aperture diaphragm Sat,a first single lens La1, a second single lens La2, a third single lensLa3, a fourth single lens La4, and an optical member GLa1 which arearrayed in order from the subject side (side of −Z direction indicatedby arrow in the drawing) along the optical axis C (Z axis). In addition,lens surfaces R1, R3, R5, and R7 shown in FIG. 11 indicateincidence-side surfaces of the single lenses La1 to La4, and lenssurfaces R2, R4, R6, and R8 indicate emission-side surfaces of thesingle lenses La1 to La4. An optical image of a subject is projectedonto the light receiving surface 21A through the imaging lens 10A.

In addition, it is preferable to dispose a cover glass, a low passfilter, or an IR cut filter on the subject side of the light receivingsurface 21A according to the configuration of an imaging system. Inconsideration of this, an example in which the optical member GLa1 thatdoes not have power and has a parallel plate shape is disposed is shownin FIG. 11. In addition, the aperture diaphragm Sat does not indicatethe shape or size but indicates the position on the optical axis Z.

Furthermore, in FIG. 11, five light rays Ja1, Ja2, Ja3, Ja4, and Ja5 areshown in order of small image height from the on-axis light ray Ja1 tothe off-axis light ray Ja5 incident at a maximum angle of view.

In addition, five MTF curves Mta20 shown in FIG. 12A indicate a changein a value of MTF characteristics in a spatial frequency of 20 Line/mmat each position where the five light rays are projected onto the lightreceiving surface 21A. Five MTF curves Mta30 shown in FIG. 12B indicatea change in a value of MTF characteristics in a spatial frequency of 30Line/mm at each position similar to that described above, five MTFcurves Mta40 shown in FIG. 12C indicate a change in a value of MTFcharacteristics in a spatial frequency of 40 Line/mm at each positionsimilar to that described above, and five MTF curves Mta50 shown in FIG.12D indicate a change in a value of MTF characteristics in a spatialfrequency of 50 Line/mm at each position similar to that describedabove.

In addition, although an example in which the optical member GLa1 isdisposed between the fourth single lens La4 and the light receivingsurface 21A is shown as the configuration example of FIG. 11, a low passfilter or various kinds of filters which cut a specific wavelengthregion may be disposed between lenses. Alternatively, surface treatment(coating) having the same operation as various filters may be performedon a lens surface of one of the first single lens La1 to the fourthsingle lens La4.

The imaging lens 10A has a first lens group GFa, which includes thethree single lenses La1, La2, and La3 and has a positive power, and asecond lens group GRa, which includes the one single lens La4 and has anegative power, in order from the object side. A lens surface R8positioned closest to the image side in the second lens group GRa has anoff-axis inflection point Qa.

In addition, as described above, an inflection point is a point on alens surface, and the inflection point in the case where a tangentialplane at this point is perpendicular to the optical axis C (Z axis) iscalled an inflection point. Moreover, an inflection point other than thepoint crossing the optical axis on the lens surface is called anoff-axis inflection point.

In the imaging lens 10A, the lens surface R8 is concave toward the imageside in the middle of the lens surface R8 and convex toward the imageside in the periphery of the lens surface R8. Moreover, the lens surfaceR8 satisfies the following conditional expression (1).

0.5H<h<H   (1)

Here, “H” is an effective radius of the lens surface R8, and “h” is adistance from the off-axis inflection point Qa of the lens surface R8 tothe optical axis.

In addition, it can be said that the distance h from the off-axisinflection point Qa of the lens surface R8 to the optical axis is aheight from the optical axis of a point on an aspheric surface where theinclination of a tangential plane with respect to a tangential plane(plane perpendicular to the optical axis) of an aspheric apex becomes 0.

In addition, the first single lens La1 positioned closest to the subjectside (side of −Z direction indicated by arrow in the drawing) among thethree single lenses La1, La2, and La3 that form the first lens group GFaof the imaging lens 10A has a positive power, and the lens surface R1 ofthe single lens La1 on the subject side is convex toward the subjectside. The second single lens La2 adjacent to the first single lens La1in the first lens group GFa has a negative power, and the lens surfaceR4 of the second single lens La2 on the image side (side of +Z directionindicated by arrow in the drawing) is convex surface toward the imageside. The third single lens La3 positioned closest to the image side inthe first lens group GFa has a positive power.

Hereinafter, design data of the imaging lens 10A in the first examplewill be described.

Lens data and various kinds of data are shown in Table 1, coefficientsof aspheric expression of each aspheric surface are shown in Table 2,and approximate specification of the imaging lens 10A is shown in Table3.

TABLE 1 Example 1 (four lenses) Surface number Ri Di Ndj νdj Aperture ∞0.119 diaphragm 1* 2.070 1.110 1.47136 76.6 2* −15.959 0.800 3* −2.1620.679 1.60595 27.0 4* −9.117 0.100 5* 6.048 1.000 1.51007 56.2 6* 29.4920.314 7* 2.160 1.100 1.51007 56.2 8* 1.782 0.700 9  ∞ 0.300 1.51633 64.110  ∞ 0.376 Image ∞ 0.000 surface

Focal length 5.277

F number 2.8

TABLE 2 Example 1 (four lenses) Surface number K A3 A4 A5 A6 11.21129740 −0.02464958 0.05275897 −0.12023671 0.05100521 2 −10.00343250−0.00475970 −0.02553074 −0.01379899 −0.01198224 3 1.55127390 −0.00118810−0.13263220 0.10838046 0.00206148 4 −9.27863960 −0.10122820 −0.114471780.12665960 0.00449924 5 −50.08963290 −0.13043949 0.06749931 0.00339300−0.01076773 6 10.02612250 −0.01717648 −0.00600583 −0.00521320−0.00090616 7 −10.06977900 0.03412823 −0.07001306 −0.00663654 0.002009068 −4.22653160 0.03095479 −0.07589071 0.02710552 −0.00354984 Surfacenumber A7 A8 A9 A10 1 0.04176113 −0.01010916 −0.04612620 0.01953189 20.00539686 0.01124139 −0.01613398 0.00437339 3 −0.04216384 0.001985170.04783041 −0.02009110 4 −0.02944682 −0.00473446 0.00920799 0.00141127 5−0.00966040 −0.00019870 0.00284438 −0.00122221 6 −0.00162871 −0.000572430.00043875 −0.00004603 7 0.00239877 −0.00064428 −0.00007006 0.00007089 8−0.00120134 0.00045058 0.00008157 −0.00003850

TABLE 3 Example 1 F number 2.8/Focal length 5.277 mm Four-lensconstruction Number of pixels Ngs corresponding to the maximum diameterDmax of an Maximum effective region of a point image, diameter which isconverted for each pixel pitch Dmax (μm) of each pixel region of anPixel Shortest effective pitch Pg = Pixel pitch Pixel pitch taking Focalregion of a 2.2 μm Pg = 1.85 μm Pg = 1.4 μm distance length point imageconversion conversion conversion Sk (mm) Sd (μm) h:H/2 10 4.5 5.7 7.126f 250 1.73:1.38 7 3.2 4.0 5.0 22f 300

As shown below the lens data of Table 1, the focal length f of theimaging lens 10A is 5.277 mm and the F number is 2.8.

In the lens data of Table 1, the surface number indicates an i-thsurface number (i=1, 2, 3, . . . ) increasing sequentially toward theimage side with a lens surface positioned closest to the subject side asa first lens surface. Moreover, in Table 1, a surface number (i=9, 10)of the optical member GLa1 is also described since the aperturediaphragm Sat and the optical member GLa1 are described together.

“Ri” of Table 1 indicates a paraxial radius of curvature of the i-thsurface (i=1, 2, 3, . . . ), and “Di” indicates a surface spacingbetween the i-th (i=1, 2, 3, . . . ) surface and the (i+1)-th surface onthe optical axis Z. “Ri” of Table 1 corresponds to the reference numeralRi (i=1, 2, 3, . . . ) in FIG. 1.

Ndj of Table 1 indicates a refractive index of a j-th (j=1, 2, 3, . . .) optical element at the d-line (wavelength of 587.6 nm), the j-thnumber (j=1, 2, 3, . . . ) increasing sequentially toward the image sidewith an optical element positioned closest to the subject side as afirst optical element. In addition, vdj of Table 1 indicates the Abbenumber of the j-th optical element with respect to the d line. In Table1, the units of paraxial radius of curvature and on-axis surface spacingis mm. In the case of the paraxial radius of curvature, a case in whichthe subject side is convex is positive and a case in which the imageside is convex is negative. In addition, the meaning of symbols in Table1 is also equal to that in examples to be described later.

In the lens data of Table 1, an aspheric surface has a surface numberadded with * mark. Each aspheric surface is defined by the followingaspheric expression.

$Z = {\frac{Y^{2}/R}{1 + ( {1 - {K \cdot {Y^{2}/R^{2}}}} )^{1/2}} + {\sum\limits_{i = 3}^{20}{AiY}^{i}}}$

Z: Aspheric depth (length of a perpendicular line from a point with theheight Y on an aspheric surface to a plane perpendicular to an opticalaxis with which an aspheric apex is in contact)

Y: height (distance from an optical axis)

R: paraxial radius of curvature

K, Ai: aspheric coefficient (i=3 to 20)

Values of coefficients K, A3, A4, A5, . . . of each aspheric surface inthe aspheric expression A are shown in Table 2.

In each of the single lenses La1 to La4 that form the imaging lens 10A,both an incidence-side lens surface and an emission-side lens surfacehave aspheric shapes.

In addition, Table 3 shows the relationship among a maximum diameterDmax of an effective region of a point image, the number of pixels(number of pixel regions) Ngs corresponding to the maximum diameter Dmaxof the effective region of the point image, a shortest taking distanceSk, and a focal depth Sd in the imaging system of Example 1.

Furthermore, the column of “h: H/2” in Table 3 indicates a distance of“h” from the optical axis to an off-axis inflection point of the lenssurface R8. In addition, “H/2” indicates a size (size of 0.5 H) of halfof the effective radius H of the lens surface R8. Here, it can be seenthat the lens surface R8 satisfies the conditional expression (1) of“0.5H<h<H”.

In addition, the pixel number Ngs in Table 3 indicates the number ofpixel regions corresponding to the maximum diameter of an effectiveregion of a point image for each pixel pitch Pg (2.2 μm, 1.85 μm, 1.4μm) in a pixel region on a light receiving surface. Here, a value of thepixel number Ngs is calculated by expression of “pixel numberNgs=maximum diameter Dmax/pixel pitch Pg”.

The maximum diameter Dmax of the effective region of the point image isa diameter of the effective region of the point image in a direction inwhich the effective region of the point image includes a largest numberof pixels, and the pixel pitch Pg is a pitch between pixel regions(light receiving pixels) in the direction.

The shortest taking distance Sk is a recommended value when an imaginglens is supplied for practical use and indicates a shortest distancefrom an imaging lens, which can project an image of a subject onto alight receiving surface with desired resolution, to the subject. Thisshortest distance is expressed as a distance (taking distance) from alens surface (here, the lens surface R1), which is positioned closest tothe imaging lens, to a subject.

This shortest taking distance is included in a range of a takingdistance allowing to obtain an effect in which the quality of image dataobtained by imaging an optical image projected onto the light receivingsurface is improved by restoration processing.

Furthermore, in imaging systems of Examples 1 to 3, the range of thetaking distance allowing to obtain an effect of improving the quality ofimage data obtained by the restoration processing is a range of a takingdistance from 0 to ∞ (point at infinity) and is an entire range in whicha subject can be photographed.

The focal depth Sd indicates a defocus range in which an image of asubject can be projected onto the light receiving surface withresolution equal to or larger than that defined when the light receivingsurface is defocused in a state where the position of the subject withrespect to the imaging lens is fixed. This focal depth Sd is a valueconsidered to correspond to the range of the taking distance, in which asubject can be projected onto the light receiving surface with anintended resolution in a state where the position of the light receivingsurface with respect to the imaging lens is fixed at an intendedposition, to some extent. That is, it is thought that a range of ataking distance in which a subject can be projected onto the lightreceiving surface with the intended resolution is increased as a valueof the focal depth Sd is increased.

In addition, the definition of aspheric expression and meaning of lensdata, various kinds of data, coefficients of aspheric expression,expression regarding approximate specification of an imaging lens,numeric values, and terms in Tables 1, 2, and 3 is equal to that in theexamples to be described later.

As can be seen from Table 3, the imaging system of Example 1 isconstructed such that a maximum diameter of an effective region of apoint image covers three or more pixel (3.2 pixels) when the effectiveregion of the point image projected onto the light receiving surface 21Ais 7 μm or more and the pixel pitch between light receiving pixels thatform the light receiving surface 21A is 2.2 μm or less.

In addition, a value of the shortest taking distance Sk is 26 f (about137 mm) when the maximum diameter Dmax of the effective region of thepoint image is set to 10 μm and is 22 f (about 116 mm) when the maximumdiameter Dmax of the effective region of and the point image is set to 7μm.

In addition, a value of the focal depth Sd of the imaging lens 10A is250 μm when the maximum diameter Dmax of the effective region of thepoint image is set to 10 μm and is 300 μm when the maximum diameter Dmaxof the effective region of and the point image is set to 7 μm.

For a value of MTF characteristics regarding the imaging system ofExample 1, when the light receiving surface 21A is made to be closest tothe imaging lens 10A, that is, when a value of defocus amount Ud inFIGS. 12A to 12D is 0, all values of MTF characteristics in a spatialfrequency of 20 to 50 Line/mm are positive values.

In addition, when the light receiving surface 21A is away from theimaging lens 10A, that is, when the value of defocus amount in FIGS. 12Ato 12D is set to 300 μm, all values of MTF characteristics in a spatialfrequency of 20 to 50 Line/mm are positive values.

That is, when the value of defocus amount is in a range of 0 to 300 μm,all values of MTF characteristics in a spatial frequency of 20 to 50Line/mm are positive values.

In a range in which the value of defocus amount is 300 μm to 400 μm, thevalue of MTF characteristics in a spatial frequency of 30 to 50 Line/mmis inverted from 0% and false resolution occurs. The range in which thefalse resolution occurs is indicated by arrow Gik in the drawing.

Here, since it can be said that image data obtained by imaging an imageof a subject projected onto a light receiving surface has opticallymeaningful information when the value of MTF characteristics regardingthe image is larger than 0%, the image data may be subjected torestoration processing in order to improve the resolution. However, inthe case where the value of MTF characteristics regarding the image ofthe subject projected onto the light receiving surface is 0% or isturned up from 0% to cause the false resolution to occur, image dataobtained by imaging the image does not have optically meaningfulinformation. Accordingly, even if the restoration processing isperformed on such image data, it is not possible to improve the quality(resolution of an image expressed by the image data) of the image data.

Thus, according to the imaging system, the value of MTF characteristicsof an image obtained by projecting a subject onto the light receivingsurface 21A can always be set to a value larger than 0% (it is possibleto prevent the false resolution from occurring) when a taking distanceis made to change in a range of 22 f to ∞ in an intended state where thepositional relationship between the light receiving surface 21A and theimaging lens 10A is fixed.

That is, an image of a subject projected onto the light receivingsurface 21A in a range of a taking distance of 0 to ∞ can be made as ameaningful image.

Moreover, since an effective region of a point image projected onto thelight receiving surface 21A when the taking distance is made to changein the range of 0 to ∞ has a size covering three or more pixels on thelight receiving surface 21A, the resolution of an image can be improvedby executing the restoration processing on image data obtained byimaging a subject existing in this range.

That is, it can be said that image data obtained by imaging an imageincluding various subjects, which are projected onto the light receivingsurface 21A through the imaging system in Example 1 and exist in a rangeof a taking distance of 22 f to ∞, satisfies a prerequisite (conditionfor improving the resolution) for executing the restoration processing.

In addition, the restoration processing can be more easily executed bysuppressing a fluctuation in the size of a point image projected ontothe light receiving surface 21A small. That is, even if an imageprojected onto the light receiving surface includes various subjectsexisting at different taking distances, for example, the restorationprocessing can be executed without changing a parameter in image dataexpressing a subject existing at any position if blur states of pointimages forming images of the subjects are equal. Thus, a burden of thesignal processing unit that executes the restoration processing can bereduced.

On the other hand, in the case of executing the restoration processingusing the same parameter all the time, the resolution of an imageexpressing a corresponding subject can be similarly improved for imagedata expressing a subject existing at any position by executing therestoration processing if blur states of point images that form imagesof various subjects, which are projected onto the light receivingsurface and exist at different taking distances, are equal. That is, byexecution of the restoration processing, the resolution of an image canbe improved uniformly over the entire image.

Thus, by designing the imaging lens 10A such that the focal depth of theimaging lens 10A is large, the resolution of the entire image expressedby image data obtained by imaging an image including various subjects,which are projected onto the light receiving surface 21A through theimaging lens 10A and exist in a range of a taking distance of 22 f to ∞,can be improved by the restoration processing.

In addition, according to the imaging lens 10A designed as describedabove, an incidence angle of light incident on the light receivingsurface 21A with respect to the light receiving surface 21A can be madesmall, that is, an imaging lens with good telecentricity can beobtained.

Hereinafter, imaging systems of Examples 2 and 3 will be described. Inaddition, since optical properties of the imaging systems in Examples 2and 3 are similar to those of the imaging system in Example 1, anexplanation thereof will be omitted.

<Regarding an Imaging System of Example 2>

FIG. 13 is a cross-sectional view showing the schematic configuration ofan imaging lens 10B including three single lenses in the second example.FIGS. 14A to 14D are views showing a change in a value (%) of MTFcharacteristics of an optical image projected onto a light receivingsurface when the light receiving surface is defocused with respect tothe imaging lens onto the coordinates in which the horizontal axisindicates a defocus amount Ud (μm) in the optical-axis direction (Z-axisdirection) of the light receiving surface and the vertical axisindicates the value (%) of MTF characteristics. Here, a defocus range ofthe light receiving surface is 400 μm.

In addition, FIGS. 14A to 14D showing the MTF characteristics of theimaging system regarding the imaging lens 10B correspond to FIGS. 12A to12D showing the MTF characteristics regarding the imaging lens 10A.

As shown in FIG. 13, the imaging lens 10B has an aperture diaphragm Sbt,a first single lens Lb1, a second single lens Lb2, a third single lensLb3, a first optical member GLb1, and a second optical member GLb2 whichare arrayed in order from the subject side (side of −Z directionindicated by arrow in the drawing) along the optical axis C (Z axis). Inaddition, lens surfaces R1, R3, and R5 shown in FIG. 13 indicateincidence-side surfaces of the single lenses Lb1 to Lb3, and lenssurfaces R2, R4, and R6 indicate emission-side surfaces of the singlelenses Lb1 to La3. An optical image of a subject is projected onto alight receiving surface 21B through the imaging lens 10B.

In addition, each of the first and second optical members GLb1 and GLb2is an optical member which is formed of a parallel plate and does nothave power.

The first and second optical members GLb1 and GLb2 which do not havepower are disposed between the third single lens Lb3 and the lightreceiving surface 21B.

Furthermore, in FIG. 13, five light rays Jb1, Jb2, Jb3, Jb4, and Jb5 areshown in order of small image height from the on-axis light ray Jb1 tothe off-axis light ray Jb5 incident at a maximum angle of view.

In addition, five MTF curves Mtb20 shown in FIG. 14A indicate a changein a value of MTF characteristics in a spatial frequency of 20 Line/mmat each position where the five light rays are projected onto the lightreceiving surface 21B. Five MTF curves Mtb30 shown in FIG. 14B indicatea change in a value of MTF characteristics in a spatial frequency of 30Line/mm at each position similar to that described above, five MTFcurves Mtb40 shown in FIG. 14C indicate a change in a value of MTFcharacteristics in a spatial frequency of 40 Line/mm at each positionsimilar to that described above, and five MTF curves Mtb50 shown in FIG.14D indicate a change in a value of MTF characteristics in a spatialfrequency of 50 Line/mm at each position similar to that describedabove.

The imaging lens 10B has a first lens group GFb, which includes the twosingle lenses Lb1 and La2 and has a positive power, and a second lensgroup GRb, which includes the one single lens Lb3 and has a negativepower, in order from the subject side. A lens surface R6 positionedclosest to the image side (side of +Z direction indicated by arrow inthe drawing) in the second lens group GRb has an off-axis inflectionpoint Qb.

In the imaging lens 10B, the lens surface R6 positioned closest to theimage side in the second lens group GRb is concave toward the image sidein the middle of the lens surface R6 and convex toward the image side inthe periphery of the lens surface R6. Moreover, the lens surface R6satisfies the above conditional expression (1) 0.5H<h<H.

In addition, the first single lens Lb1 positioned on the subject side(side of −Z direction indicated by arrow in the drawing) of the twosingle lenses Lb1 and La2 that form the first lens group GFb has apositive power, and the lens surface R1 of the single lens Lb1 on thesubject side is convex surface toward the subject side. In the secondsingle lens Lb2 of the first lens group GFb positioned on the imageside, the image-side surface R4 of the single lens Lb2 is convex towardthe image side.

Hereinafter, design data of the imaging lens 10B in the second examplewill be described.

Lens data and various kinds of data are shown in Table 4, coefficientsof aspheric expression of each aspheric surface are shown in Table 5,and approximate specification of the imaging lens 10B is shown in Table6. In addition, “Ri” of Table 4 and the reference numeral “Ri” in FIG.13 correspond to each other.

TABLE 4 Example 2 (three lenses) Surface number Ri Di Ndj νdj Aperture ∞−0.120 diaphragm 1* 1.445 0.791 1.53114 55.4 2* −3.395 0.223 3* −1.5600.764 1.63178 23.2 4* −11.065 0.234 5* 1.703 0.960 1.53114 55.4 6* 1.3340.396 7  ∞ 0.495 1.52000 55.0 8  ∞ 0.244 Image surface ∞ 0.000

Focal length 3.312

F number 2.7

TABLE 5 Example 2 (three lenses) Surface number K A3 A4 A5 A6 30.12852990 0.00976249 −0.03207688 −0.16317950 0.33466830 4 0.09999990−0.03023295 −0.20760347 −0.06072193 −0.21300370 5 0.10063060 0.07041734−0.65685088 0.00282485 1.80528090 6 0.09999950 −0.05637836 −0.772172390.03211432 2.38962630 7 0.03061670 −0.14017100 −0.88195617 0.010644770.95719211 8 0.04380360 −0.03479559 −0.36508266 −0.01863131 0.26961061Surface number A7 A8 A9 A10 A11 3 0.07278352 −1.00740680 −0.474703253.41529050 −3.16337050 4 0.05253407 0.02422838 −0.03140656 0.09130447−0.23804840 5 0.28010794 −7.67023220 0.16190599 19.86376700 −0.503370096 0.00339539 −5.71596040 0.08306921 10.35335700 0.03386329 7 0.01726570−0.80297213 −0.00067235 0.40314453 0.00388345 8 0.03974424 0.14562228−4.22996350 24.18613900 −82.26362800 Surface number A12 A13 A14 A15 A163 −14.25336100 5.61940790 64.11670800 3.13869750 −154.71176000 40.36479431 0.92530303 0.16338034 1.31874660 −1.09966870 5 −26.23953800−0.07354199 14.72031400 2.25487560 0.40902761 6 −11.67464600 −0.054499956.27414510 −0.11930784 2.16706530 7 −0.02324472 0.00733302 −0.027218050.00632184 −0.00035338 8 187.43373000 −300.18131000 345.61445000−287.81496000 171.95004000 Surface number A17 A18 A19 A20 3 −1.58385650210.54242000 −49.25468100 −105.14658000 4 0.07820894 2.68233770−16.16748300 8.80290720 5 2.07996040 −5.56428710 −8.63704520 4.821745606 −0.09071725 −4.49242640 0.05916245 1.59162020 7 0.00058318 −0.00054253−0.00431963 −0.00138795 8 −71.87173800 19.95655700 −3.306869600.24744736

TABLE 6 Example 2 F number 2.7/Focal length 3.312 mm Three-lensconstruction Maximum Number of pixels Ngs corresponding to diameter themaximum diameter Dmax of an Dmax effective region of a point image,which is (μm) of an converted for each pixel pitch of each effectivepixel region Shortest Focal region of a Pixel pitch Pixel pitch Pixelpitch taking length point Pg = 2.2 μm Pg = 1.85 μm Pg = 1.4 μm distanceSd image conversion conversion conversion Sk (mm) (μm) h:H/2 7 3.2 4.05.0 16f 250 0.96:0.865

In each of the lenses that form the imaging lens 10B, both anincidence-side lens surface and an emission-side lens surface haveaspheric shapes.

In addition, as shown below the lens data of Table 4, the focal length fof the imaging lens 10B is 3.312 mm and the F number is 2.7.

In addition, since meaning of lens data, various kinds of data,coefficients of aspheric expression, expression regarding approximatespecification of an imaging lens, numeric values, and terms in Tables 4,5, and 6 is equal to that in Tables 1, 2, and 3 in Example 1, anexplanation thereof will be omitted.

As can be seen from Table 6, the imaging system of Example 2 isconstructed such that a maximum diameter of an effective region of apoint image covers three or more pixel (3.2 pixels) when the effectiveregion of the point image projected onto the light receiving surface 21Bis 7 μm or more and the pixel pitch between light receiving pixels thatform the light receiving surface 21B is 2.2 μm or less.

In addition, a value of the shortest taking distance Sk is 16 f (about53 mm) when the maximum diameter Dmax of the effective region of thepoint image is set to 7 μm.

This shortest taking distance is included in a range of a takingdistance allowing to obtain an effect in which the quality of image dataobtained by imaging an optical image projected onto the light receivingsurface is improved by restoration processing.

A value of the focal depth Sd of the imaging lens 10B is 250 μm when themaximum diameter Dmax of the effective region of the point image is setto 7 μm.

For a value of MTF characteristics regarding the imaging system of thesecond example, when the light receiving surface 21B is made to beclosest to the imaging lens 10B, that is, when a value of defocus amountUd in FIGS. 14A to 14D is 0 μm, all values of MTF characteristics in aspatial frequency of 20 to 50 Line/mm are positive values.

In addition, when the light receiving surface 21B is away from theimaging lens 10B, that is, when the value of defocus amount in FIGS. 14Ato 14D is set to 250 μm, all values of MTF characteristics in a spatialfrequency of 20 to 50 Line/mm are 5% or more. In a range in which thevalue of defocus amount is 250 μm to 400 μm, all values of MTFcharacteristics in a spatial frequency of 20 to 50 Line/mm are invertedfrom 0% and false resolution occurs. The range in which the falseresolution occurs is indicated by arrow Gik in the drawing.

That is, when the value of defocus amount Ud is in a range of 0 μm to250 μm (in the range of a focal depth), all values of MTFcharacteristics in a spatial frequency of 20 to 50 Line/mm are positivevalues.

As described above, according to the imaging system in Example 2, thevalue of MTF characteristics in a comparatively wide defocus range(about 250 μm) becomes a positive value.

Thus, according to the imaging system in Example 2, the value of MTFcharacteristics of an image obtained by projecting a subject onto thelight receiving surface 21B can always be set to a value larger than 0%(it is possible to prevent the false resolution from occurring) when ataking distance is made to change in a range of 0 to ∞ in an intendedstate where the positional relationship between the light receivingsurface 21B and the imaging lens 10B is fixed.

That is, an image of a subject projected onto the light receivingsurface 21B in a range of a taking distance of 16 f to ∞ can be made asa meaningful image.

Moreover, since an effective region of a point image projected onto thelight receiving surface 21B when the taking distance is made to changein the range of 16 f to ∞ has a size covering three or more pixels onthe light receiving surface 21B, the resolution of an image can beimproved by executing the restoration processing on image data obtainedby imaging a subject existing in this range. That is, it can be saidthat image data expressing subjects, which are obtained through theimaging system in Example 2 and exist in a range of a taking distance of0 to ∞, satisfies a prerequisite (condition for improving theresolution) for executing the restoration processing.

Thus, by designing the imaging lens 10B such that the focal depth of theimaging lens 10B is large, the resolution of the entire image expressedby image data obtained by simultaneously imaging images of varioussubjects, which exist in a range of a taking distance of 16 f to ∞, bythe restoration processing.

In addition, when the imaging system of Example 2 is supplied forpractical use, the taking distance is preferably limited to ten times(about 33 mm (10 f)) or more of a focal length. More preferably, thetaking distance is limited to 53 mm (16 f) as described above.

Thus, if the taking distance is limited to the range of 33 mm to ∞, alarge effect of increasing the resolution of an image by executing therestoration processing on image data obtained by imaging an image of asubject can be acquired. Thus, if the taking distance is limited to therange of 53 mm to ∞, a larger effect of increasing the resolution of animage by executing the restoration processing on image data obtained byimaging an image of a subject can be acquired.

In addition, according to the imaging lens 10B of Example 2 designed asdescribed above, an incidence angle of light incident on the lightreceiving surface 21B with respect to the light receiving surface 21Bcan be made small, that is, an imaging lens with good telecentricity canbe obtained like the case in Example 1.

<Regarding an Imaging System of Example 3>

FIG. 15 is a cross-sectional view showing the schematic configuration ofan imaging lens 10C including three single lenses in Example 3. FIGS.16A to 16D are views showing a change in a value (%) of MTFcharacteristics of an optical image projected onto a light receivingsurface when the light receiving surface is defocused with respect tothe imaging lens onto the coordinates in which the horizontal axisindicates a defocusing amount Ud (μm) in the optical-axis direction(Z-axis direction) of the light receiving surface and the vertical axisindicates the value (%) of MTF characteristics. Here, a defocus range ofthe light receiving surface is 400 μm.

In addition, FIGS. 16A to 16D showing the MTF characteristics regardingthe imaging lens 10C correspond to FIGS. 12A to 12D showing the MTFcharacteristics regarding the imaging lens 10A.

As shown in FIG. 15, the imaging lens 10C has an aperture diaphragm Sct,a first single lens Lc1, a second single lens Lc2, a third single lensLc3, and an optical member GLc1 which are arrayed in order from thesubject side (side of −Z direction indicated by arrow in the drawing)along the optical axis C (Z axis).

In addition, lens surfaces R1, R3, and R5 shown in FIG. 15 indicateincidence-side surfaces of the single lenses Lc1 to Lc3, and lenssurfaces R2, R4, and R6 indicate emission-side surfaces of the singlelenses Lc1 to Lc3. An optical image of a subject is projected onto thelight receiving surface 21C through the imaging lens 10C.

The optical member GLc1 is an optical member which is formed of aparallel plate and does not have power.

Furthermore, in FIG. 15, five light rays Jc1, Jc2, Jc3, Jc4, and Jc5 areshown in order of small image height from the on-axis light ray Jc1 tothe off-axis light ray Jc5 incident at a maximum angle of view.

In addition, five MTF curves Mtc20 shown in FIG. 16A indicate a changein a value of MTF characteristics in a spatial frequency of 20 Line/mmat each position where the five light rays are projected onto the lightreceiving surface 21C. Five MTF curves Mtc30 shown in FIG. 16B indicatea change in a value of MTF characteristics in a spatial frequency of 30Line/mm at each position similar to that described above, five MTFcurves Mtc40 shown in FIG. 16C indicate a change in a value of MTFcharacteristics in a spatial frequency of 40 Line/mm at each positionsimilar to that described above, and five MTF curves Mtc50 shown in FIG.16D indicate a change in a value of MTF characteristics in a spatialfrequency of 50 Line/mm at each position similar to that describedabove.

The imaging lens 10C has a first lens group GFc, which includes the twosingle lenses Lc1 and Lc2 and has a positive power, and a second lensgroup GRc, which includes the one single lens Lc3 and has a negativepower, in order from the subject side. A lens surface R6 positionedclosest to the image side in the second lens group GRc has an off-axisinflection point Qc.

In the imaging lens 10C, the lens surface R6 positioned closest to theimage side in the second lens group GRc is concave toward the image sidein the middle of the lens surface R6 and convex toward the image side ofthe lens surface R6 in the periphery. Moreover, the lens surface R6satisfies the above conditional expression (1) 0.5H<h<H.

In addition, the first single lens Lc1 positioned on the subject side ofthe two single lenses Lc1 and Lc2 that form the first lens group GFc hasa positive power, and the lens surface R1 of the single lens Lc1 on thesubject side is convex toward the subject side. In the second singlelens Lc2 of the first lens group GFc positioned on the image side, theimage-side surface R4 of the single lens Lc2 is convex toward the imageside.

Hereinafter, design data of the imaging lens 10C Example 3 will bedescribed.

Lens data and various kinds of data are shown in Table 7, coefficientsof aspheric expression of each aspheric surface are shown in Table 8,and approximate specification of the imaging lens 10C is shown in Table9. In addition, “Ri” of Table 7 and the reference numeral “Ri” in FIG.15 correspond to each other.

TABLE 7 Example 3 (three lenses) Surface number Ri Di Ndj νdj Aperture ∞−0.120 diaphragm 1* 1.445 0.791 1.53114 55.4 2* −3.395 0.223 3* −1.5600.764 1.63178 23.2 4* −11.065 0.234 5* 1.703 0.960 1.53114 55.4 6* 1.3340.396 7  ∞ 0.495 1.52000 55.0 8  ∞ 0.244 Image surface ∞ 0.000

Focal length 4.043

F number 3.5

TABLE 8 Example 3 (three lenses) Surface number K A3 A4 A5 A6 11.46821160 −0.02006750 −0.01716269 −0.07488272 −0.00807329 2 5.912461400.03858523 −0.00390848 0.00521844 0.42149785 3 2.68478870 −0.01203839−0.03769086 −0.00672518 −0.10003112 4 −22.94585750 −0.262567730.06660669 −0.05308108 0.03934465 5 −4.05769940 −0.31290897 −0.029075100.05714552 0.02834143 6 −3.33611150 −0.11799765 0.09043585 0.08521950−0.00370655 Surface number A7 A8 A9 A10 1 0.20927058 −0.00396025−0.39769240 0.03759849 2 0.16034238 −0.77511754 −1.93911820 3.57739830 3−0.04142547 0.12137291 0.16117261 −0.24036373 4 −0.01863391 0.016549030.02453973 −0.01496812 5 −0.01023398 −0.00261078 0.00553029 −0.002512026 −0.01246110 −0.00340986 0.00410789 −0.00065698

TABLE 9 Example 3 F number 3.5/Focal length 4.043 Three-lensconstruction Number of pixels Ngs corresponding to Maximum the maximumdiameter Dmax of an diameter effective region of a point image, which isDmax (μm) converted for each pixel pitch of each of an pixel regionShortest Focal effective Pixel pitch Pixel pitch Pixel pitch takinglength region of a Pg = 2.2 μm Pg = 1.85 μm Pg = 1.4 μm distance Sdpoint image conversion conversion conversion Sk (mm) (μm) h:H/2 10 4.55.7 7.1 15f 350 1.04:0.94

In each of the lenses that form the imaging lens 10C, both anincidence-side lens surface and an emission-side lens surface haveaspheric shapes.

In addition, as shown below the lens data of Table 7, the focal length fof the imaging lens 10C is 4.043 mm and the F number is 3.5.

In addition, since meaning of lens data, various kinds of data,coefficients of aspheric expression, expression regarding approximatespecification of an imaging lens, numeric values, and terms in Tables 7,8, and 9 is equal to that in Tables 1, 2, and 3 in the Example 1, anexplanation thereof will be omitted.

As can be seen from Table 9, the imaging system of Example 3 isconstructed such that a maximum diameter of an effective region of apoint image covers three or more pixel (4.5 pixels) when the effectiveregion of the point image projected onto the light receiving surface 21Cis 10 μm or more and the pixel pitch between light receiving pixels thatform the light receiving surface 21C is 2.2 μm or less.

In addition, a value of the shortest taking distance Sk is 15 f (about60 mm) when the maximum diameter Dmax of the effective region of thepoint image is set to 10 μm.

This shortest taking distance is included in a range of a takingdistance allowing to obtain an effect in which the quality of image dataobtained by imaging an optical image projected onto the light receivingsurface is improved by restoration processing.

A value of the focal depth Sd of the imaging lens 10C is 350 μm when themaximum diameter Dmax of the effective region of the point image is setto 10 μm.

Moreover, for a value of MTF characteristics regarding the imagingsystem of Example 3, when the light receiving surface 21C is made to beclosest to the imaging lens 10C, that is, when a value of defocus amountUd in FIGS. 16A to 16D is 0 μm, all values of MTF characteristics in aspatial frequency of 20 to 50 Line/mm are positive values.

In addition, when the light receiving surface 21C is away from theimaging lens 10C, that is, when the value of defocus amount in FIGS. 16Ato 16D is set to 300 μm, all values of MTF characteristics in a spatialfrequency of 20 to 50 Line/mm are several percents or more. In a rangein which the value of defocus amount is 300 μm to 400 μm, the value ofMTF characteristics in a spatial frequency of 30 to 50 Line/mm isinverted from 0% and false resolution occurs.

As described above, according to the imaging system in Example 3, thevalue of MTF characteristics in a comparatively wide defocus range(about 300 μm) becomes a positive value.

Thus, according to the imaging system, the value of MTF characteristicsof an image obtained by projecting a subject onto the light receivingsurface 21C can always be set to a value larger than 0% (it is possibleto prevent the false resolution from occurring) when a taking distanceis made to change in a range of 15 f to ∞ in an intended state where thepositional relationship between the light receiving surface 21C and theimaging lens 10C is fixed.

That is, an image of a subject projected onto the light receivingsurface 21C in a range of a taking distance of 15 f to ∞ can be made asa meaningful image.

Moreover, since an effective region of a point image projected onto thelight receiving surface 21C when the taking distance is made to changein the range of 15 f to ∞ has a size covering three or more pixels onthe light receiving surface 21C, the resolution of an image can beimproved by executing the restoration processing on any image dataobtained by imaging a subject existing at any position. That is, it canbe said that all image data obtained through the imaging system ofExample 3 satisfies a prerequisite (condition for improving theresolution) for executing the restoration processing.

Thus, by designing the imaging lens 10C such that the focal depth of theimaging lens 10C is large, the resolution of the entire image expressedby image data obtained by simultaneously imaging images of varioussubjects, which exist in a range of a taking distance of 15 f to ∞, canbe improved by the restoration processing.

Thus, if the taking distance is limited to the range of 60 mm to ∞, alarger effect of increasing the resolution of an image by executing therestoration processing on image data obtained by imaging an image of asubject can be acquired.

In addition, according to the imaging lens 10C of Example 3 designed asdescribed above, an incidence angle of light incident on the lightreceiving surface 21C with respect to the light receiving surface 21Ccan be made small, that is, an imaging lens with good telecentricity canbe obtained like the case in Example 1.

<Aberrations of Imaging Lenses in Examples 1 to 3>

FIG. 17 is a view showing an aberration of the imaging lens 10A, FIG. 18is a view showing an aberration of the imaging lens 10B, and FIG. 19 isa view showing an aberration of the imaging lens 10C. Each of aberrationviews of the imaging lenses in Examples 1 to 3 shows sphericalaberration, astigmatism, distortion, and lateral chromatic aberration inorder from above in FIGS. 17 to 19.

Although each aberration figure shows aberrations at the e-line(wavelength of 546.07 nm) as a reference wavelength, aberrations at theF-line (wavelength of 486.1 nm) and the C-line (wavelength of 656.3 nm)are also shown in the spherical aberration figure and the lateralchromatic aberration figure. The distortion figure shows an amount ofdeviation from an ideal image height when the ideal image height is setto f×tan θ using focal length f and half angle of view θ (variable;0≦θ≦ω) of the whole system.

<Imaging System of a Comparative Example>

Hereinafter, a known imaging lens used in a portable cellular phonecamera and the like will be described as a comparative example.

FIG. 20 is a cross-sectional view showing the schematic configuration ofan imaging lens including four single lenses in the comparative example.FIGS. 21A to 21D are views showing a change in a value (%) of MTFcharacteristics of an optical image projected onto a light receivingsurface when the light receiving surface is defocused with respect tothe imaging lens onto the coordinates in which the horizontal axisindicates a defocusing amount Ud (μm) in the optical-axis direction(Z-axis direction) of the light receiving surface and the vertical axisindicates the value (%) of MTF characteristics. Here, a defocus range ofthe light receiving surface is 400 μm.

In addition, FIGS. 21A to 21D showing the MTF characteristics correspondto FIGS. 12A to 12D showing the MTF characteristics regarding theimaging lens 10A.

As shown in FIG. 20, an imaging lens 10H in the comparative example hasa first single lens Lh1, a second single lens Lh2, a third single lensLh3, a fourth single lens Lh4, and an optical member GLh1 which arearrayed in order from the subject side (side of −Z direction indicatedby arrow in the drawing) along the optical axis C (Z axis). The imaginglens 10H having these four single lenses is designed such that the depthof field increases.

An optical image of a subject is projected onto the light receivingsurface 21H through the imaging lens 10H.

In addition, the optical member GLh1 is an optical member which isformed of a parallel plate and does not have power.

Furthermore, in FIG. 20, five light rays Jh1, Jh2, Jh3, Jh4, and Jh5 areshown in order of small image height from the on-axis light ray Jh1 tothe off-axis light ray Jh5 incident at a maximum angle of view.

In addition, five MTF curves Mth20 shown in FIG. 21A indicate a changein a value of MTF characteristics in a spatial frequency of 20 Line/mmat each position where the five light rays are projected onto the lightreceiving surface 21H. Five MTF curves Mth30 shown in FIG. 21B indicatea change in a value of MTF characteristics in a spatial frequency of 30Line/mm at each position similar to that described above, five MTFcurves Mth40 shown in FIG. 21C indicate a change in a value of MTFcharacteristics in a spatial frequency of 40 Line/mm at each positionsimilar to that described above, and five MTF curves Mth50 shown in FIG.21D indicate a change in a value of MTF characteristics in a spatialfrequency of 50 Line/mm at each position similar to that describedabove.

For the value of MTF characteristics in the imaging system of thecomparative example, when the light receiving surface is made to beclose to the imaging lens, that is, when a value of the defocus amountis in a range of approximately 0 to 120 μm in FIGS. 21A to 21D, thevalue of MTF characteristics in a spatial frequency of 30 to 50 Line/mmis inverted from 0%, resulting in a state where the false resolutionoccurs. The range in which the false resolution occurs is indicated byarrow Gik in the drawing.

In addition, when the light receiving surface is made to be close to theimaging lens, that is, when a value of the defocus amount is in a rangeof approximately 280 to 400 μm in FIGS. 21A to 21D, the value of MTFcharacteristics in a spatial frequency of 30 to 50 Line/mm is invertedfrom 0%, resulting in a state where the false resolution occurs. Therange in which the false resolution occurs is indicated by arrow Gik inthe drawing.

Here, the value of MTF characteristics in a range in which a value ofthe defocus amount Ud is 120 μm to 280 μm (value of focal depth) is apositive value, and a range of fluctuation in value of MTFcharacteristics in each spatial frequency is about 85% (50 Line/mm), 90%(40 Line/mm), 70% (30 Line/mm), and 45% (20 Line/mm).

As described above, according to the imaging system in the comparativeexample, the value of MTF characteristics is a positive value only in acomparatively narrow defocus range (range of about 160 μm). Accordingly,the amount of fluctuation in the value of MTF characteristics is large.

In a defocus range (indicated by arrow Gik in the drawing) where thevalue of MTF characteristics is inverted from 0%, a point image hasfalse resolution and an optically meaningful image which can bespecified that the effective region covers three or more pixels cannotbe obtained.

In other words, only in a considerably limited range of a takingdistance, the value of MTF characteristics is a positive value, that is,an image of a subject projected onto the light receiving surface can bemade as a meaningful image. In addition, the amount of fluctuation inthe size of a point image projected onto the light receiving surface islarge.

Moreover, since the imaging system in the comparative example is notconstructed such that an effective region of a point image projectedonto the light receiving surface when changing the taking distance in arange of 0 to ∞ has a size covering three or more pixels on the lightreceiving surface, image data obtained through the imaging system doesnot satisfy a prerequisite (condition for improving the resolution) forexecuting the restoration processing.

For this reason, even if the restoration processing is performed on theimage data obtained by imaging an image of a subject projected onto thelight receiving surface 21H through the imaging system in thecomparative example, an effect of improving the resolution of the imageexpressing the subject cannot be acquired.

In addition, cases in which imaging lenses are limited in various kindsof conditions have been described in the examples. However, since animaging lens having a first lens group, which includes at least one lensand has a positive power, and a second lens group, which includes atleast one lens and in which a lens positioned closest to the image sidehas a negative power, in order from the object side is used as theimaging lens in the imaging system of the invention, the number oflenses included in each group, the shapes of the lenses, and the likeare not limited.

1. An imaging system comprising: an imaging lens; an imaging device thathas a light receiving surface on which a plurality of light receivingpixels are two-dimensionally arrayed and that forms first image datebased on an optical image of a subject projected onto the lightreceiving surface through the imaging lens and outputs the first imagedata corresponding to the subject; a coefficient storage section thatwill store a restoration coefficient corresponding to a state of a pointimage, which is projected onto the light receiving surface through theimaging lens and is expressed by the first image data output from theimaging device, when a maximum diameter of an effective region of thepoint image is a size covering three or more pixels; and a signalprocessing section that executes restoration processing on the firstimage data by using the restoration coefficient, the restorationprocessing being executed to generate second image data equivalent tothe first image data output from the imaging device when the resolvingpower of the imaging lens is higher, wherein the signal processingsection executes the restoration processing in a condition where a pixelregion covering total nine or more pixels including three or more pixelsin a vertical direction and three or more pixels in a horizontaldirection on the light receiving surface is set as a minimum unit, andthe imaging lens comprises: in order from an object side of the imaginglens, a first lens group which includes at least one lens and has apositive power; and a second lens group which includes at least one lensand in which a lens positioned closest to an image side of the imaginglens has a negative power.
 2. The imaging system according to claim 1,wherein the coefficient storage section will store the restorationcoefficient individually calculated for each corresponding imagingsystem.
 3. The imaging system according to claim 1, wherein thecoefficient storage section will store the restoration coefficient whichis selected corresponding to a state of the point image expressed by thefirst image data among candidates of restoration coefficientscorresponding to respective states of point images classified into aplurality of types.
 4. The imaging system according to claim 1, whereinthe coefficient storage section will store a correction-completedrestoration coefficient obtained by further correction of therestoration coefficient according to a state of the point imageexpressed by the first image data, the restoration coefficient beingselected corresponding to the state of the point image among candidatesof a plurality of types of restoration coefficients corresponding torespective states of point images classified into a plurality of types.5. The imaging system according to claim 1, further comprising: arestoration coefficient acquisition section that acquires therestoration coefficient and stores the acquired restoration coefficientin the coefficient storage section.
 6. The imaging system according toclaim 1, wherein the signal processing section executes the restorationprocessing with a minimum pixel region which includes an entireeffective region of the point image projected onto the light receivingsurface, as a minimum unit.
 7. The imaging system according to claim 1,wherein the signal processing section executes the restorationprocessing such that a size of an effective region of the point image inan image expressed by the second image data is smaller than a size of aneffective region of the point image in an image expressed by the firstimage data.
 8. The imaging system according to claim 1, wherein a lenssurface positioned closest to the image side in the second lens grouphas an off-axis inflection point.
 9. The imaging system according toclaim 1, wherein a lens surface positioned closest to the image side inthe second lens group is concave toward the image side an on-axis of thelens surface and convex toward the image side in a periphery of the lenssurface.
 10. The imaging system according to claim 8, wherein a lenssurface of a lens positioned closest to the image side in the secondlens group satisfies conditional expression (1):0.5H<h<H   (1) wherein H is an effective radius of the lens surfacepositioned closest to the image side in the second lens group, and h isa distance from an off-axis inflection point of the lens surfacepositioned closest to the image side in the second lens group to anoptical axis of the imaging lens.
 11. The imaging system according toclaim 1, wherein the imaging lens includes three single lenses.
 12. Theimaging system according to claim 11, wherein the first lens groupincludes two single lenses, wherein one positioned on the object sideamong the two single lenses has a positive power and an object-sidesurface of the one is convex toward the object side, and the otherpositioned on the image side among the two single lenses has animage-side surface convex toward the image side, and the second lensgroup includes one single lens.
 13. The imaging system according toclaim 1, wherein the imaging lens includes four single lenses.
 14. Theimaging system according to claim 13, wherein the first lens groupincludes three single lenses and, wherein a first one positioned closestto the object side among the three single lenses has a positive powerand an object-side surface of the first single lens is convex toward theobject side, a second one adjacent to the first single lens among thethree single lenses has a negative power and an image-side surface ofthe second single lens is convex toward the image side, and a third onepositioned closest to the image side among the three single lenses has apositive power, and the second lens group includes one single lens. 15.An imaging apparatus comprising all imaging system according to claim 1.16. A portable terminal apparatus comprising an imaging system accordingto claim
 1. 17. An onboard apparatus comprising an imaging systemaccording to claim
 1. 18. A medical apparatus comprising an imagingsystem according to claim
 1. 19. An imaging system comprising: animaging lens; an imaging device that has a light receiving surface onwhich a plurality of light receiving pixels are two-dimensionallyarrayed and that forms first image date based on an optical image of asubject projected onto the light receiving surface through the imaginglens and outputs the first image data corresponding to the subject; acoefficient storage section that stores a restoration coefficientcorresponding to a state of a point image, which is projected onto thelight receiving surface through the imaging lens and is expressed by thefirst image data output from the imaging device, when a maximum diameterof an effective region of the point image is a size covering three ormore pixels; and a signal processing section that executes restorationprocessing on the first image data by using the restoration coefficient,the restoration processing being executed to generate second image dataequivalent to the first image data output from the imaging device whenthe resolving power of the imaging lens is higher, wherein the signalprocessing section executes the restoration processing in a conditionwhere a pixel region covering total nine or more pixels including threeor more pixels in a vertical direction and three or more pixels in ahorizontal direction on the light receiving surface is set as a minimumunit, and the imaging lens comprises: in order from an object side ofthe imaging lens, a first lens group which includes at least one lensand has a positive power; and a second lens group which includes atleast one lens and in which a lens positioned closest to an image sideof the imaging lens has a negative power.
 20. A method for manufacturingan imaging system that includes: an imaging lens, wherein the imaginglens comprises: in order from an object side of the imaging lens, afirst lens group which includes at least one lens and has a positivepower; and a second lens group which includes at least one lens and inwhich a lens positioned closest to an image side of the imaging lens hasa negative power; an imaging device that has a light receiving surfaceon which a plurality of light receiving pixels are two-dimensionallyarrayed and that forms first image data based on an optical image of asubject projected onto the light receiving surface through the imaginglens and outputs the first image data expressing the subject; acoefficient storage section that stores a restoration coefficientcorresponding to a state of a point image, which is projected onto thelight receiving surface through the imaging lens and is expressed by thefirst image data output from the imaging device, when a maximum diameterof an effective region of the point image is a size covering three ormore pixels; and a signal processing section that executes restorationprocessing on the first image data by utilizing the restorationcoefficient, the restoration processing being executed to generatesecond image data equivalent to the first image data output from theimaging device when a resolving power of the imaging lens is higher,wherein the signal processing section executes the restorationprocessing in a condition where a pixel region covering total nine ormore pixels including three or more pixels in a vertical direction andthree or more pixels in a horizontal direction on the light receivingsurface is set as a minimum unit, the method comprising projecting thepoint image onto the light receiving surface of the imaging devicethrough the imaging lens to cause the coefficient storage section tostore the restoration coefficient corresponding to a state of the pointimage expressed by the first image data output from the imaging device.21. The method of manufacturing an imaging system according to claim 20,wherein the restoration coefficient is individually calculated for eachcorresponding imaging system.
 22. The method of manufacturing an imagingsystem according to claim 21, wherein the restoration coefficient isselected corresponding to a state of the point image expressed by thefirst image data among candidates of each restoration coefficientcorresponding to each of states of point images classified into aplurality of types.
 23. The method of manufacturing an imaging systemaccording to claim 20, wherein the restoration coefficient is obtainedby further correction of the restoration coefficient according to astate of the point image expressed by the first image data, therestoration coefficient being selected corresponding to the state of thepoint image among candidates of a plurality of types of restorationcoefficients corresponding to respective states of point imagesclassified into a plurality of types.